Physics Engine Revamp

[JackErb]

Stress test collisions,
Separate static and dynamic entities & check collisions accordingly,
Introduce "feet" hitbox for dynamic entities to more accurately detect landing,
Stress test of fixed points

[JackErb]

Dedicated landing hitbox for dynamic entities to properly detect when landing on the ground.

HandleCollision() should have access to the polygons that collided so can do additional positional checks (I.e. vert_check, horiz_check