feat(ngAnimate): provide support for animator animation callbacks

prior to this feature, there was no way to detect when an animation has completed
when using $animator inside directives. An optional "done" callback function
can be provided to each animation method which is fired once the animation has
completed or when a new animation takes place on the same element.

BREAKING CHANGE: in $animator, all public-facing instance methods have
been changed to accept a final callback function argument:

Use the following animation instance methods when performing animations
inside of directives:
animator.enter(element, parent, after, done);
animator.leave(element, done);
animator.move(element, parent, after, done);
animator.show(element, done);
animator.hide(element, done);
animator.animate(event, element, done);
feat(ngAnimate): provide support for addClass and removeClass animation handlers