Added a debug bool used in mesh generation to AABBTree Node

AABBTree nodes now have a bool value to state if they were in a
colllision prior to generating the mesh. This allows visual debugging
for collision detection.
Implemented AABBTree::CollisionCheck

CollisionCheck() will check if a sphere of a given radius intersects
with a node in the AABBTree.

A helper method AABBSphereTest has been added to make the actual check.

Reduced the AABB halfsize back to 2.5 as our AABB's are 5 units to match
the current room size.
Move AABBTree into the Sigma namespace
Added AABBTree to SimplePhysics