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.
need to add streaming because memory is too small to store all lines
initial test of PD control in physics server, need to switch to PD control for motor constraint, instead of using external forces.
only allow server to create and initialize shared memory,
client will report failure
intercept signals to cleanup shared memory in standalone app, thanks to
Roland Philippsen.
