BulletSim: add physical object initialized flag so updates and collisions
don't happen until the object is completely initialized.

This fixes the problem of doing a teleport while the simulator is running.
The destruction of the physical object while the engine is running means
that the physics parameter update would overwrite the new position of the
newly created avatar.
BulletSim: include check for volume detect in check for zeroing avatar motion.

Normally, avatar motion is zeroed if colliding with a stationary object so
they don't slide down hills and such. Without volume detect check this also
allowed avatars to stand on volume detect objects and to have some jiggling
when they were in the volume detect object. This commit fixes both.