Add first pass of help panel

This is just an idea really.

The help plugin is only included in the tw5.com wiki; the idea is to
also include it in the empty.html wiki, either as a plugin or as part
of the core.

If it stays as a plugin, the idea would be to have different help
plugins for different languages.

plugins/tiddlywiki/help/HelpPanel.tid

@@ -0,0 +1,12 @@
+title: $:/plugins/tiddlywiki/help/HelpPanel
+tags: $:/tags/PageTemplate
+
+<$reveal type="match" state="$:/config/ShowHelp" text="yes">
+<div class="tc-help-panel">
+<div class="tc-tiddler-controls">
+<$button set="$:/config/ShowHelp" setTo="no" class="tc-btn-invisible">{{$:/core/images/close-button}}</$button> ''Help''
+</div>
+<<tabs "[all[shadows+tiddlers]tag[$:/tags/HelpPanel]!has[draft.of]]" "$:/plugins/tiddlywiki/help/HelpPanel/Support" "$:/state/tab/help">>
+</div>
+</$reveal>
+