Add option to have VehicleSpeed used everywhere we use rpm/mph

[nyetwurk]

Currently, all acceleration/HP calculations are based on RPM and a user supplied rpm per mph.

This requires the user to supply a rpm per mph.

Using Velocity (if supplied by the log instead) would eliminate that requirement

However

• Velocity is often very inaccurate, either by design, or because the car is not stock
• Velocity often suffers the same quantization effects that RPM does

So this feature might be of limited use.