refactor($animate): use $animate.$$setClassImmediately to save code

The only difference between adding the classes synchronously this way, and doing it the regular way, is that you don't get all of the `-add-active`, `-add`, `-remove-active`, `-remove` gunk added.

We can do it asynchronously without adding those. We can also do it asynchronously and just make sure that those operations get flushed before the structural animation is fiinished. None of that really matters.