Select and multi-select now responsive to labels

When labels change value select and multi-select will now both update
both their sort order and filtering. This is accomplished by filtering
and sorting through a proxy which is updated whenever the
labelValuePath is updated.
Select widgets can now be <TAB> selected

Added focusIn and focusOut handlers and tabindex, so that when you tab
to focus the select widget, it expands the widget.

Closes #104
Close popover when the user hits escape and fix not calling callbacks on
escape press in modal dialog