Add more flexible support for static content

Passing the static content through the `$:/core/templates/html-tiddler`
template made it impossible to produce output that wasn’t HTML encoded
(eg stylesheets).

core/templates/raw-static-tiddler.tid

@@ -0,0 +1,7 @@
+title: $:/core/templates/raw-static-tiddler
+
+<!--
+
+This template is used for saving tiddlers as static HTML
+
+--><$view field="text" format="plainwikified" />

core/templates/static.area.tid

@@ -1,6 +1,7 @@
 title: $:/core/templates/static.area
 
 <$reveal type="nomatch" state="$:/isEncrypted" text="yes">
+{{{ [all[shadows+tiddlers]tag[$:/tags/RawStaticContent]!has[draft.of]] ||$:/core/templates/raw-static-tiddler}}}
 {{$:/core/templates/static.content||$:/core/templates/html-tiddler}}
 </$reveal>
 <$reveal type="match" state="$:/isEncrypted" text="yes">