Mistakenly, I had changed the tiddler widget to refresh itself when the
value of the target tiddler changed. This is not in fact necessary; it
only needs to refresh itself when the identity of the target tiddler
changes.
Fixes#744
Getting rid of the old widget mechanism files finally gives us a payoff
for all the refactoring. Still a bit of tidying up to do, and we need
to re-introduce the animation mechanisms.
Belatedly realised that the design would be clearer without these two
separate concepts being conflated into a single widget.
As a result of this change, any other widget or template that generates
transclude widgets has needed adjustment.
