Make edit preview pane extensible

Additional preview panes are tagged “$:/tags/EditPreview“. A dropdown
is shown if there is more than one edit preview loaded.

core/language/en-GB/EditTemplate.multids

@@ -5,6 +5,8 @@ Body/Hint: Use [[wiki text|http://tiddlywiki.com/static/WikiText.html]] to add f
 Body/Placeholder: Type the text for this tiddler
 Body/Preview/Button/Hide: hide preview
 Body/Preview/Button/Show: show preview
+Body/Preview/Type: preview type:
+Body/Preview/Type/Output: output
 Field/Remove/Caption: remove field
 Field/Remove/Hint: Remove field
 Fields/Add/Button: add

core/ui/EditTemplate/Preview/output.tid

@@ -0,0 +1,9 @@
+title: $:/core/ui/EditTemplate/body/preview/output
+tags: $:/tags/EditPreview
+caption: {{$:/language/EditTemplate/Body/Preview/Type/Output}}
+
+<$set name="tv-tiddler-preview" value="yes">
+
+<$transclude />
+
+</$set>

core/ui/EditTemplate/body.tid

@@ -20,15 +20,24 @@ tags: $:/tags/EditTemplate
 
 <$reveal state="$:/state/showeditpreview" type="match" text="yes">
 
-<em class="tc-edit"><<lingo Hint>></em> <$button type="set" set="$:/state/showeditpreview" setTo="no"><<lingo Preview/Button/Hide>></$button>
+<em class="tc-edit"><<lingo Hint>></em> <$button type="set" set="$:/state/showeditpreview" setTo="no"><<lingo Preview/Button/Hide>></$button> <$list filter="[all[shadows+tiddlers]tag[$:/tags/EditPreview]!has[draft.of]butfirst[]limit[1]]" variable="listItem">
+<em class="tc-edit"><<lingo Preview/Type>></em> <$select tiddler="$:/state/editpreviewtype" default="$:/core/ui/EditTemplate/body/preview/output">
+<$list filter="[all[shadows+tiddlers]tag[$:/tags/EditPreview]!has[draft.of]]">
+<option value=<<currentTiddler>>>{{!!caption}}</option>
+</$list>
+</$select>
+
+</$list>
 
 <div class="tc-tiddler-preview">
 <div class="tc-tiddler-preview-preview">
-<$set name="tv-tiddler-preview" value="yes">
 
-<$transclude />
+<$transclude tiddler={{$:/state/editpreviewtype}} mode="inline">
+
+<$transclude tiddler="$:/core/ui/EditTemplate/body/preview/output" mode="inline"/>
+
+</$transclude>
 
-</$set>
 </div>
 
 <div class="tc-tiddler-preview-edit">