Added ability to set ratio of a CVT

Users can now directly set the gear ratio of a CVT.  For example, this allows use of custom algorithms for CVT ratio, E2 controlled CVTs that act as 6 speed gearboxes with multiple settings (sport, race, etc), and dual-CVT tank turning via different ratios.  Set the ratio to 0 or negative for the CVT to resume using target min/max rpm calculations for ratio.