PyBullet: add option to cache graphics shapes for URDF files, handy for benchmarks with many duplicate robots

See https://github.com/erwincoumans/pybullet_robots ANYmal.py for an example.
PyBullet: Expose p.setPhysicsEngineParameter(solverResidualThreshold=1e-2) (b3PhysicsParamSetSolverResidualThreshold), increases solver performance a lot
PyBullet: Expose p.setPhysicsEngineParameter(contactSlop) Set it to zero, to avoid issues with restitution.
PyBullet: Expose isNumpyEnabled, return True is PyBullet was compiled with NUMPY support for 'getCameraImage'.
PyBullet: Expose p.ChangeDynamics(objectUid, linkIndex, contactProcessingThreshold), to avoid issues of speculative/predictive contacts with restitution.
See also http://twvideo01.ubm-us.net/o1/vault/gdc2012/slides/Programming%20Track/Vincent_ROBERT_Track_ADifferentApproach.pdf

examples/Importers/ImportURDFDemo/URDF2Bullet.h

@@ -3,6 +3,8 @@
 #include "LinearMath/btAlignedObjectArray.h"
 #include "LinearMath/btTransform.h"
 #include <string>
+#include "UrdfJointTypes.h"//for UrdfMaterialColor cache
+
 class btVector3;
 class btTransform;
 class btMultiBodyDynamicsWorld;
@@ -26,15 +28,25 @@ enum ConvertURDFFlags {
   CUF_USE_IMPLICIT_CYLINDER=128,
   CUF_GLOBAL_VELOCITIES_MB=256,
   CUF_MJCF_COLORS_FROM_FILE=512,
+  CUF_ENABLE_CACHED_GRAPHICS_SHAPES = 1024,
 };
 
+struct UrdfVisualShapeCache
+{
+	btAlignedObjectArray<UrdfMaterialColor> m_cachedUrdfLinkColors;
+	btAlignedObjectArray<int> m_cachedUrdfLinkVisualShapeIndices;
+};
+
+
 void ConvertURDF2Bullet(const URDFImporterInterface& u2b,
 			MultiBodyCreationInterface& creationCallback,
 			const btTransform& rootTransformInWorldSpace,
 			btMultiBodyDynamicsWorld* world,
 			bool createMultiBody,
 			const char* pathPrefix,
-            int flags = 0);
+            int flags = 0,
+			UrdfVisualShapeCache& cachedLinkGraphicsShapes= UrdfVisualShapeCache()
+			);
 
 
 #endif //_URDF2BULLET_H