Added reset link option to UI

I've noticed that in some cases on the web, selects don't have an appropriate "None" option, but users need the ability to set their selection to null. I've added an optional parameter that creates a little "x" link users can click to clear out the select value and input.

New options:

* reset: add reset link. Defaults to false.
* class_reset: class for the reset element. Defaults to 'reset'.