The main point of this change is to streamline the core
code for input pills, and we use also modify user groups.
The main change to input_pill.js is that you now
configure a function called `create_item_from_text`, and
that can return an arbitrary object, and it just needs
a field called `display_value`.
Other changes:
* You now call `input.create(opts)` to create the
widget.
* There is no longer a cache, because we can
write smarter code in typeahead `source` functions
that exclude ids up front.
* There is no value/optinalKey complexity, because
the calling code can supply arbitrary objects and
do their own external data management on the pill
items.
* We eliminate `prependPill`.
* We eliminate `data`, `keys`, and `values`, and just
have `items`.
Steve Howell