Simplify GJK. Still needs double precision for large differences of feature scales.

Extract faces directly from btConvexHullComputer (in initializePolyhedralFeatures), instead of reconstructing them, thanks to Josh Klint in #1654
PyBullet: use initializePolyhedralFeatures for convex hulls and boxes (to allow SAT)
PyBullet: expose setPhysicsEngineParameter(enableSAT=0 or 1) to enable Separating Axis Test based collision detection for convex vs convex/box and convex versus concave triangles (in a triangle mesh).

examples/SharedMemory/SharedMemoryPublic.h

@@ -797,6 +797,7 @@ struct b3PhysicsSimulationParameters
 	int m_jointFeedbackMode;
 	double m_solverResidualThreshold;
 	double m_contactSlop;
+	int m_enableSAT;
 };