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/SharedMemoryCommands.h

@@ -455,6 +455,7 @@ enum EnumSimParamUpdateFlags
 	SIM_PARAM_UPDATE_DEFAULT_FRICTION_CFM = 1048576,
 	SIM_PARAM_UPDATE_SOLVER_RESIDULAL_THRESHOLD = 2097152,
 	SIM_PARAM_UPDATE_CONTACT_SLOP = 4194304,
+	SIM_PARAM_ENABLE_SAT = 8388608,
 };
 
 enum EnumLoadSoftBodyUpdateFlags