fix(modal): Support close animation 

Closes #1341

Notes:

I'm not using the `$transition` method itself to create any transitions. I'm actually using the transition module just to determine if the browser supports transitions. Checking for transition support isn't actually necessary as modal still closes within 500ms due to the timeout fallback mechanism.

I understand that it's a little hacky that I did a `removeClass('in')` within the remove logic instead of attempting to change the `scope.animate`. However, changing the scope.animate for the modal isn't trivial as the modelWindow directive is using an isolate scope. Since the scope has been destroyed, there won't be a conflict between states, the ng-class on modelBackdrop and modelWindow directives no longer have any effect.