Organising community content
Add mechanisms to the reference docs
Clarify "Editions"

@giffmex - sorry I should have been clearer. We’ll only call things an
“Edition” if it is distributed via tiddlywiki.com. So for instance your
NoteStormTW should be listed under “Resources” until it’s been bought
into tiddlywiki.com.

We’ve already had the situation where people who have built editions
(and indeed plugins) haven’t been able to keep them up to date with the
latest versions of the core. So I want to draw a clear distinction
between those things that are part of the main distribution, and have
some guarantee of long term support and those things that are
distributed independently.