more refactoring, removed PhysicsInterface, cleaned up demos to make use of btDynamicsWorld derived classes.

removed two cached optimizations, type in btTransform and cached inverse transform (todo: test performance impact)
committed fixes that make the code adhere to 'who creates it, also destroys it'

Demos/BspDemo/BspConverter.cpp

@@ -15,7 +15,6 @@ subject to the following restrictions:
 
 #include "BspConverter.h"
 #include "BspLoader.h"
-#include "CcdPhysicsEnvironment.h"
 #include "LinearMath/btVector3.h"
 
 void BspConverter::convertBsp(BspLoader& bspLoader,float scaling)