Copter: add coax heli support

Motors should be attached to RCOutputs 1 and 2, Flaps should be connected
to RC outputs 3 and 4
Coax: remove unused servo3, servo4

Removed commented out code
Copter: moved coax servo set-up to AP_MotorCoax
Copter: removed unused servo3, servo4 from coax
Coax: servos to ch1, ch2, motors to ch3, ch4
Copter: coax allows ch5 and higher for do_set_servo cmd
Copter: bug fix for duplicate single and coax params
AP_TECS : Fixed bug preventing accel launch detection when not using AS sensor
TradHeli: disable aux channels 7 and 8
Copter: disable aux channel ch7 for Tri
Copter: disable aux channel 7 for SingleCopter

Move servo range setup to AP_MotorsSingle
Copter: disable aux channels used for motors
Copter: remove setup_aux_channels

moved to individual motors libraries
Copter: correct release note dates
Update 3DR_X8_RTF.param

Updated RATE_PIT_(P,I,D), RATE_RLL_(P,I,D), RATE_YAW_(P,I,D), THR_MID, and STB_(PIT, RLL, and YAW) to autotuned param values

Grant Lieberman
3D Robotics
Iris: Updated gimbal configuration
Copter: version to AC3.2-dev
OptFlow: update function added to fix compiler error
AP_InertialSensor: use fixed size arrays

apparently helps SITL build on MacOS
AHRS: add update_trig

Calculates helper trig values including cos_roll, cos_pitch