Add warning box while editing a shadow tiddler

This addresses the third line item of issue #570

TODO: The filter is not working.
TODO: The message is too genaric and needs help.

core/language/en-GB/EditTemplate.multids

@@ -4,6 +4,7 @@ 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/ShadowWarning: You are editing a shadow tiddler. Any changes will override the default version.
 Fields/Add/Button: add
 Fields/Add/Name/Placeholder: field name
 Fields/Add/Prompt: Add a new field:

core/ui/EditTemplate/body.tid

@@ -2,6 +2,14 @@ title: $:/core/ui/EditTemplate/body
 tags: $:/tags/EditTemplate
 
 \define lingo-base() $:/language/EditTemplate/
+<$list filter="[all[current]is[shadow]]">
+<div class="tw-message-box">
+
+<<lingo Body/ShadowWarning>>
+
+</div>
+</$list>
+
 <$reveal state="$:/ShowEditPreview" type="match" text="yes">
 
 <em class="tw-edit"><<lingo Body/Hint>></em> <$button type="set" set="$:/ShowEditPreview" setTo="no"><<lingo Body/Preview/Button/Hide>></$button>