TradHeli: add landing collective min
TradHeli: use landing collective when landed or landing
TradHeli: Use Leaky Integrator on Yaw Rate controller

Use when rotor is not running to prevent the rudder from slowly moving over
TradHeli: add support for drive tail rotors

Repurposed external gyro and made it multi-funcitonal.
required PWM on Ch8 to start the motor in RSC Mode moved up from 100 to 400. This is to facilitate two-stage switching of the motors with PWM>100 starting the tail motor, and PWM>400 starting the main motor.
Additional amendments by Randy
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: 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
Copter: add deadzone to ch8 for TradHeli
Copter: remove unused init_rate_controllers
TradHeli: move pilot desired rotor speed to heli.pde
TradHeli: ext gyro gain range 0 to 1000
TradHeli: add RSC_RUNUP_TIME param and rotor speed estimate
TradHeli: move STAB_COL_MIN to main parameter list
TradHeli: angle error to zero while motors runup

Set angle error to zero in get_roll_rate_stabilized_bf,
get_pitch_rate_stabillize_bf, get_yaw_rate_stabilized_bf.
Original commit by Rob Lefebvre
TradHeli: remove calls to get_manual_collective in auto throttle

set_collective_for_landing method makes this unnecessary
TradHeli: set throttle_min to zero by default