refactor(dropdown): remove isolated scope

Closes #1818
feat(typeahead): add WAI-ARIA markup

Closes #1814
refactor(accordion): transclude function in compile is deprecated.

Closes #1789
refactor(carousel): use `track by` in template

Closes #1723
feat(button): Allow radio button uncheck

btn-radio with uncheck attribute acts as a hybrid checkbox/radio-button, selecting exclusively among the button set, but also allowing the selected item to be unselected, leaving the button set without a selected item.