Added support for separating axis test for polyhedral shapes

Added initial support for polyhedral contact clipping. 
This clipping takes a separating normal, that can be computed using either SAT or GJK/EPA.
To enable clipping, use btPolyhedralConvexShape::initializePolyhedralFeatures(); (needs to be enabled for both convex shapes)
No concave trimesh support for SAT/clipping yet. To enable SAT, see the toggle in btConvexConvexAlgorithm.
Fixes in contact normal in btGjkPairDetector. Hopefully this doesn't cause any regression (we need unit tests!)

src/BulletCollision/CollisionShapes/btPolyhedralConvexShape.h

@@ -18,18 +18,32 @@ subject to the following restrictions:
 
 #include "LinearMath/btMatrix3x3.h"
 #include "btConvexInternalShape.h"
+class btConvexPolyhedron;
 
 
 ///The btPolyhedralConvexShape is an internal interface class for polyhedral convex shapes.
 class btPolyhedralConvexShape : public btConvexInternalShape
 {
+	
 
 protected:
 	
+	btConvexPolyhedron* m_polyhedron;
+
 public:
 
 	btPolyhedralConvexShape();
 
+	virtual ~btPolyhedralConvexShape();
+
+	///optional method mainly used to generate multiple contact points by clipping polyhedral features (faces/edges)
+	virtual bool	initializePolyhedralFeatures();
+
+	const btConvexPolyhedron*	getConvexPolyhedron() const
+	{
+		return m_polyhedron;
+	}
+
 	//brute force implementations
 
 	virtual btVector3	localGetSupportingVertexWithoutMargin(const btVector3& vec)const;