CVS simuv2 transmission/inertia/differential fixes

Committed the previously discussed patch fixing the inertia of the whole
drivetrain and the differentials.

Main Visible Changes:

Inertia
-------
When power-spinning, it takes longer for the wheels to spin _and_ to
spin down.

Inertia is maintained when changing gears and using the clutch, so you
can make even under-powered cars spin in this way if you really want to.

NOTE: The increased inertia may require some robots to increase their
braking settings somewhat. So check your robots.


Differential
------------
The Free and Limited Slip differentials have changed to be closer to
reality.  The Free differential is 100% OK.  However, the Limited Slip
differential is only one of many possible choices.  (The old limited
slip differential was in fact a Locking differential, which I have now
moved to a new category).

Minor changes
-------------
There was a double 'rolling resistance' line in car.cpp - I removed one
of them.


PLEASE TEST!




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