Toggle engines

Adds ability to toggle individual engines in vehicle control menu, when more than one engine present. Choice brings up submenu listing all engines. Velocities, noise and fuel usage update accordingly.
If velocity after toggling is higher than the new safe velocity, the cruise control speed is lowered.

~~TODO: make radiators only work if the engine they are attached to is enabled~~
This line (441) toggles engines on or off. It first fetches the state of the engine, and inverts it.