Iteration 6 cleanup

This branch is dedicated to refactoring the `Entity` and `CompositeHitbox` classes so that they're more readable and extensible relative to last iteration.  

These refactorings have made it easy to add support for an 'anchor point' as well, which will allow for manual specification of the 'focus' of an image through the hitbox files.  This addition will remove the issues associated with the changing camera on player animation.

These refactorings have also made it possible to add 'intangible' hitboxes, which will allow for the behavior of the mega monster to be implemented.