HitBox and other updates

Added a HitBox class, used to make boxes around entities and detects of
two entities boxes are colliding.

Reworked player/entity to have more stuff in entity. Things like
rendering are now found in entity (every entity needs to render).

Added a mob class that extends entity. Currently uses same animations as
player, and there is only one instance of the class (should be a list of
mobs later).

Added some more attributes for entities, such as health and damage.

Reworked collision a bit (more logisitical rework). Still have issues
with up collision and entity to entity collision isn't working.