Fix typo
Respect "storytop" metric when in narrow layout

Previously we were only respecting it when in the wide layout
Allow shadow tiddlers to appear in table of contents macro
Transclude the caption field in toc macro

For consistency with the way that tabs work.

To see this in action, on tiddlywiki.com open the tiddler
`$:/tags/ControlPanel` and edit it to add the tag “TableOfContents”.
You’ll see the control panel appear at the bottom of the table of
contents.
Documentation tweaks

@erwanm I ended up making some fairly extensive tweaks.

One issue is that the (excellent) material you’ve provided on
transclusion with templates covers very much the same ground as the
existing TemplateTiddlers tiddler. The existing text was focused on
transclusion with widgets; I think your material using transclusion
notation is much easier to understand.

I’ve also removed the exercises section. We don’t have exercises
elsewhere in the documentation, so I think we need to make a conscious
decision about whether we’re going to try to add them, and then do so
consistently across the material.

I also made some changes to bring the text into house style for
consistency (which I’ve also tried to start documenting).
Removing debugging statements from popup mechanism