AP_MotorsHeli: Few semantic changes in preparation for new RSC Mode.
AP_MotorsHeli: Initial implementation of RSC Mode 3 for Throttle Curve.
TradHeli: Add RSC Mode 3 Throttle Curve handling to heli.pde
AP_MotorsHeli: Slight rearrangement of rotor_ramp() to reuse function for Throttle Curve Slew.
AP_MotorsHeli: Add throttle damper feature to RSC Mode 3.
AP_MotorsHeli: Fix time scaling for Rotor Runup.
AP_MotorsHeli: Create new parameters for controlling throttle servo of a gas/nitro engine.