Copter: sanity check throttle deadzone
Plane: analog range finder limit problem fixed

There was no conversion from meters to centimeters when comparing for
limits. Also added compare to min/max for all sensor types.
Plane: Added mixing feature to range finders

When we have two range finders with overlapping regions they are mixed
in this region. Data is output with distance_cm() method. Added
parameter _MIX_EN to enable this feature.
AP_NavEKF : Reduce ripple in estimates that can cause copter motor 'pulsing'

This patch reduces the level of 5Hz and 10Hz 'pulsing' heard in motors due to GPS and altimeter fusion which cause a small 5Hz and 10Hz ripple on the output under some conditions. Attitude, velocity and position state corrections from GPS, altimeter and magnetometer measurements are applied incrementally in the interval from receiving the measurement to the predicted time of receipt of the next measurement. Averaging of attitude state corrections is not performed during periods of rapid rotation.

Time stamps are now explicitly initialised to the current IMU time to avoid unwanted activation of timeout logic on filter start and the various calls to the hal.scheduler->millis() object have been consolidated.

Unused variables have been removed
Copter: enable mount control with channels > 8 for radios with SBUS.
Cherry pick

RangeFinder, EKF Ripple, RC Channels
Lost Buzzer
Buzzer Conflict
Range finder mix bug fix
Revert "Range finder mix bug fix"

This reverts commit bf21ef76c045bdce62dc8baa6abb7a1b768a8292.
Undo Revert
Config change