Fix problems with building single-file wiki using external-js template

* core/templates/external-js/tiddlywiki5-external-js.html.tid,
  core/templates/external-js/save-all-external-js.tid,
  core/templates/external-js/save-offline-external-js.tid
  core/templates/external-js/load-external-js.tid:
  Fix #5343. Exclude client-server plugins in tiddler imports and to
  specify a working URL for loading tiddlywiki5.js from local disk.
  Mirror save/all and save/offline templates in the regular server
  edition.

  Fix #4717 (tiddlywiki5-external-js.html.tid)

* core/modules/saver-handler.js:
  Need the change to make single file autosave work with the external-js
  template.

* editions/server-external-js/tiddlywiki.info:
  Provide external-js related build targets.

* core/language/en-GB/Snippets/ExtJSReadme.tid:
  Temporary doc to supplement TW5.com's external-js section. Demonstrate
  that upgrade could be done on single-file wikis with an externalized
  TW core.

* core/language/en-GB/Snippets/GetTiddlyWikiJS.tid:
  Documentation. Meant to be included in every wiki and to help end
  users acquire tiddlywiki5.js.

core/language/en-GB/Snippets/ExtJSReadme.tid

@@ -0,0 +1,15 @@
+title: $:/language/Snippets/ExtJSReadme
+
+Additions to ~TiddlyWiki documentation [[Using the external JavaScript template|https://tiddlywiki.com/#Using%20the%20external%20JavaScript%20template]]:
+
+To ensure that the "save snapshot for offline use" button saves a working wiki, it is also necessary to set the tiddler $:/config/SaveWikiButton/Template to contain <code>~$:/core/save/<b>offline-external-js</b></code>. You must also save a copy of  "tiddlywiki5.js" in the same folder as your offline wiki file. See [[How to obtain tiddlywiki5.js|$:/language/Snippets/GetTiddlyWikiJS]] for details.
+
+!! Upgrading
+
+Upgrading an offline wiki with an external-js template will be a three-step process:
+
+# Follow the standalone file ~TiddlyWiki Upgrading process. Your wiki will be converted to a full standalone version.
+
+# Open $:/language/Snippets/GetTiddlyWikiJS tiddler from your newly upgraded wiki and click the "Export tiddlywiki5.js" button.
+
+# Verify that $:/config/SaveWikiButton/Template still contains `$:/core/save/offline-external-js`. Save your wiki again and the wiki will be converted to using the external-js template.

core/language/en-GB/Snippets/GetTiddlyWikiJS.tid

@@ -0,0 +1,54 @@
+title: $:/language/Snippets/GetTiddlyWikiJS
+
+To obtain "tiddlywiki5.js" for your offline external-js ~TiddlyWiki, use one of the following methods:
+<ul>
+
+<$reveal state="$:/plugins/tiddlywiki/tiddlyweb!!plugin-type" type="match" text="plugin">
+
+<li>
+If you are running ~TiddlyWiki on node.js, you can download <a class="tc-tiddlylink" href="%24%3A%2Fcore%2Ftemplates%2Ftiddlywiki5.js" download="tiddlywiki5.js">tiddlywiki5.js</a> from your server.
+</li>
+
+</$reveal>
+<$set name=isButtonOff filter="[[$:/boot/boot.js]is[missing]then[yes]else[no]]">
+<$set name=cssState filter="""[[$:/boot/boot.js]is[missing]then[background-color:#a9a9a9]]""" select="0">
+
+<li>
+
+If this wiki's ~TiddlyWiki core has not been externalized, you can click the following button to export "tiddlywiki5.js" from your own wiki:
+<div><$button style=<<cssState>> class="tc-btn-big-green" disabled=<<isButtonOff>> >
+<$wikify name="site-title" text={{$:/config/SaveWikiButton/Filename}}>
+<$action-sendmessage $message="tm-download-file" $param="$:/core/templates/tiddlywiki5.js" filename="tiddlywiki5.js"/>
+</$wikify>
+{{$:/core/images/download-button}} Export tiddlywiki5.js
+</$button></div>
+
+</li>
+
+</$set></$set>
+
+<li>
+
+If you have created your wiki from the "server-external-js" edition, then you can run the command:
+
+```
+tiddllywiki <your-wiki-folder> --build tiddlywiki5.js
+```
+
+File "tiddlywiki5.js" will be saved in the`output` folder within your wiki-folder.
+
+</li>
+<li>
+
+From the command line, run:
+
+```
+tiddlywiki <your-wiki-folder> \
+    --rendertiddler '$:/core/templates/tiddlywiki5.js' \
+    tiddlywiki5.js text/plain
+```
+
+File "tiddlywiki5.js" will be saved in the`output` folder within your wiki-folder.
+
+</li>
+</ul>

core/modules/saver-handler.js

@@ -157,7 +157,8 @@ SaverHandler.prototype.saveWiki = function(options) {
 		return false;
 	}
 	var	variables = options.variables || {},
-		template = options.template || "$:/core/save/all",
+		template = options.template || 
+		           this.wiki.getTiddlerText("$:/config/SaveWikiButton/Template", "$:/core/save/all"),
 		downloadType = options.downloadType || "text/plain",
 		text = this.wiki.renderTiddler(downloadType,template,options),
 		callback = function(err) {

core/templates/external-js/load-external-js.tid

@@ -0,0 +1,3 @@
+title: $:/core/templates/load-external-js
+
+&lt;script src="<<coreURL>>" onerror="alert('Error: Cannot load tiddlywiki5.js');">&lt;/script>

core/templates/external-js/save-all-external-js.tid

@@ -4,4 +4,5 @@ title: $:/core/save/all-external-js
 \define saveTiddlerFilter()
 [is[tiddler]] -[prefix[$:/state/popup/]] -[prefix[$:/temp/]] -[prefix[$:/HistoryList]] -[status[pending]plugin-type[import]] -[[$:/core]] -[[$:/boot/boot.css]] -[type[application/javascript]library[yes]] -[[$:/boot/boot.js]] -[[$:/boot/bootprefix.js]] +[sort[title]] $(publishFilter)$
 \end
+\define coreURL() %24%3A%2Fcore%2Ftemplates%2Ftiddlywiki5.js
 {{$:/core/templates/tiddlywiki5-external-js.html}}

core/templates/external-js/save-offline-external-js.tid

@@ -0,0 +1,8 @@
+title: $:/core/save/offline-external-js
+
+\import [[$:/core/ui/PageMacros]] [all[shadows+tiddlers]tag[$:/tags/Macro]!has[draft.of]]
+\define saveTiddlerFilter()
+[is[tiddler]] -[prefix[$:/state/popup/]] -[prefix[$:/temp/]] -[prefix[$:/HistoryList]] -[status[pending]plugin-type[import]] -[[$:/core]] -[[$:/plugins/tiddlywiki/filesystem]] -[[$:/plugins/tiddlywiki/tiddlyweb]] -[[$:/boot/boot.css]] -[type[application/javascript]library[yes]] -[[$:/boot/boot.js]] -[[$:/boot/bootprefix.js]] +[sort[title]] $(publishFilter)$
+\end
+\define coreURL() tiddlywiki5.js
+{{$:/core/templates/tiddlywiki5-external-js.html}}

core/templates/external-js/tiddlywiki5-external-js.html.tid

@@ -2,7 +2,7 @@ title: $:/core/templates/tiddlywiki5-external-js.html
 
 \rules only filteredtranscludeinline transcludeinline
 <!doctype html>
-{{$:/core/templates/MOTW.html}}<html lang="`<$text text={{{ [{$:/language}get[name]] }}}/>`">
+{{$:/core/templates/MOTW.html}}<html lang="{{{ [{$:/language}get[name]] }}}">
 <head>
 <meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
 <!--~~ Raw markup for the top of the head section ~~-->
@@ -43,5 +43,6 @@ title: $:/core/templates/tiddlywiki5-external-js.html
 <!--~~ Raw markup for the bottom of the body section ~~-->
 {{{ [all[shadows+tiddlers]tag[$:/tags/RawMarkupWikified/BottomBody]] ||$:/core/templates/raw-static-tiddler}}}
 </body>
-<script src="%24%3A%2Fcore%2Ftemplates%2Ftiddlywiki5.js" onerror="alert('Error: Cannot load tiddlywiki.js');"></script>
+<!--~~ Load external JS ~~-->
+{{$:/core/templates/load-external-js}}
 </html>

editions/server-external-js/tiddlywiki.info

@@ -13,11 +13,14 @@
 		"listen": [
 			"--listen","root-tiddler=$:/core/save/all-external-js"],
 		"index": [
-			"--rendertiddler","$:/plugins/tiddlywiki/tiddlyweb/save/offline","index.html","text/plain"],
+			"--rendertiddler","$:/core/save/offline-external-js","index.html","text/plain",
+			"--rendertiddler","$:/core/templates/tiddlywiki5.js","tiddlywiki5.js","text/plain"],
 		"static": [
 			"--rendertiddler","$:/core/templates/static.template.html","static.html","text/plain",
 			"--rendertiddler","$:/core/templates/alltiddlers.template.html","alltiddlers.html","text/plain",
 			"--rendertiddlers","[!is[system]]","$:/core/templates/static.tiddler.html","static","text/plain",
-			"--rendertiddler","$:/core/templates/static.template.css","static/static.css","text/plain"]
+			"--rendertiddler","$:/core/templates/static.template.css","static/static.css","text/plain"],
+		"tiddlywiki5.js": [
+			"--rendertiddler","$:/core/templates/tiddlywiki5.js","tiddlywiki5.js","text/plain"]
 	}
 }