Fix u2.Select Design

[kgrgreer]

Select was just meant to be a wrapper for the raw tag, but with 'data' binding. It is now a ChoiceView, which was not the intent. Revert Select to just a simple select tag and make a new ChoiceView to replace it. Probably move tag-level elements like Select and Input to a 'tag' sub-package. ChoiceViewTrait requires that it's users be u2.View's, so it should just be an AbstractChoiceView instead as this will avoid user-error of trying to use it in Elements. @shepheb @adamvy

[bshepherdson]

See #510.

[bshepherdson]

Done by #510 and 71db38b.