The new importvariables widget imports macro/variable definitions from
the specified tiddlers and makes them available to its children.
Allows us to split PageMacros up into separate tiddlers.
We still support loading macros from $:/core/ui/PageMacros to help
people upgrading.
Fixes#644 and #559
Astonishingly, the templates have accidentally omitted the opening tag
for some time. There were no ill effects, because browsers obligingly
add it back in when parsing
Templates are the low-level bits and pieces that allow TW5 to generate
HTML and CSS renderings of tiddlers. The UI folder contains the
user-visible UI of TW5
What we have at the moment isn't really the same as TiddlyWiki
classic's shadow tiddlers, it's a much simpler system for excluding
tiddlers. We'll use the term "shadow" instead to refer to the way that
tiddlers in plugins behave, which is exactly like TiddlyWiki classic's
shadow tiddlers.
Thus introducing a few functional regressions, but it's going to be
easier to fix things up without the old code knocking around and
getting in the way.
