TradHeli: COLYAW not applied when the motor is not running
TradHeli: ch6 tuning of ext gyro to use control_in

This could also be used to control the other Heli Ch7 functions (direct drive tail rotor control).  This should be tidied up.

Credit: Jolyon Saunders
TradHeli: BugFix to ColYaw

Credit to Jolyon Saunders for finding this bug.
TradHeli: rename rc_8 to rc_rotor
TradHeli: ramp up changes

Rewrote tail and main rotor ramp up methods
Moved direct drive ESC speed control into rsc_control method
Pass in ch7 servo as servo_aux to TradHeli motors object constructor
split CH7_SETPOINT parameter into GYR_GAIN and DIRECTDRIVE parameters
replaced RSC_RATE with uint8_t RSC_RAMP_TIME parameter
rename GOV_SETPOINT parameter to RSC_SETPOINT
RSC_MODE parameter description updated to indicate it controls the
source of main rotor speed
TradHeli: integrate constructor changes to main code
Copter: log TradHeli ch7, ch8 in MOT message
TradHeli: output to ESC drops immediately when ramping down
Copter: add deadzone to ch8 for TradHeli
Copter: remove unused init_rate_controllers
TradHeli: move pilot desired rotor speed to heli.pde

tail_rotor_runup_complete method made private
removed unused _motor_runup_timer
TradHeli: ext gyro gain range 0 to 1000

Direct Drive variable pitch tail ESC speed default to 500