Filling hole between subclass and superclass.

Subclasses no longer need to be 4-byte aligned at the end. Any gaps
between a superclass and its subclasses will be filled in by halfword
or byte fields if possible.

Refactored the alignment and shuffling methods to use a priority queue
in order to reduce the amount of logic when laying out objects.

Change-Id: Ifed71af534e0c5e77bb14555c44b973fe66df6da