fix in b3HashString
remove many unused dependencies from kuka_grasp_block_playback.py (time,math, datetime ,numpy,pylab ,sys, os, fnmatch,argparse were not used!)
move block_grasp_log.bin from Bullet3/data to Bullet3/examples/pybullet/examples/data folder.
PhysicsServerCommandProcessor, derive from CommandProcessorInterface to prepare for different back-end implementation
Expose COV_ENABLE_VR_RENDER_CONTROLLERS, to enable/disable rendering of controllers (and some frames) in VR
Expose COV_ENABLE_RENDERING to enable/disable rendering.
Fix some multi-threading issues (potential crashes), related to debug drawing/rendering in one thread, while changing the dynamics world/removing/resetSimulation in a different thread.
add UDP network connection for physics client <-> server.
also set spinning friction in rolling friction demo (otherwise objects may keep on spinning forever)