BulletSim: extend BSActorLockAxis to allow locking linear movement in
addition to angular movement. Not enabled by anything yet.
BulletSim: simplify parameter specification by reducing the number of
specifications required for simple properties with defaults.
BulletSim: remove friction calcuation from BSMotor and move linear and
angular friction computation into linear and angular movement code.
The friction wasn't being applied properly. This will make it so vehicles
don't drift as much and the drift is tunable by changing the friction
timescales.