vocab widget: added 'narrow' mode, which resulted in a fairly hefty
refactor of the widget. 'search' and 'narrow' modes are now handled
by a subclass of a VocabHandler js object/interface, which provides
some rudimetary helper routines.

The codebase is still a bit messy. Need to clean up:
  - settings (split by mode?)
  - validation (push back to VocabHandler, subclasses provide rules?)

And of course the plugin documentation needs updating.
vocab widget: minor changes to demo page
vocab widget: updated proxy for rifcs testing