AP_NavEKF : Fix bug in initial East mag field state variance
Frame_Parameters: Added Skywalker
Frame_params: Updated 3DR Quad for Tarot Gimbal
Frame_params: Updated 3DR X8 for Tarot Gimbal
Frame_params: Updated 3DR Y6B for Tarot Gimbal
Frame_params: Updated 3DR Iris for Tarot Gimbal
Plane: improved RC failsafe handling

this forces all primary control inputs to the trim value on loss of RC
input, and reduces the timeout for loss of RC input to 1 second from 2
Copter: re-enable CLI for Pixhawk
Copter: bug fix display of PerfMon log's num long loops
Git: ignore /ArduCopter/test.ArduCopter directory
Plane: fixup throttle trim on failsafe
Plane: treat PWM below 900 as invalid for mode switch

the FrSky X8R receiver will briefly give a PWM of 874 on channel 5
when connection is lost to the transmitter. We need to ensure this
doesn't cause a mode switch
Rover: fix for X8R receiver on SBUS in failsafe

the X8R briefly gives PWM of 874 on all channels when the receiver is
setup as "no pulses" failsafe handling. This was interpreted as switch
position 0, which was AUTO for me.

This change rejects pulse widths below 900 for mode changes
GPS: added set_secondary() function

for preventing notify updates for 2nd GPS
Plane: set 2nd GPS as secondary
Copter: set 2nd GPS as secondary
Rover: set 2nd GPS as secondary
Flymaple: RCOUtput disable_ch() now supports disabling outputs
AntennaTracker: now supports mavlink arm and disarm commands to disable antenna servo outputs
AntennaTracker: finish adding GPS support, including using relative or absolute altitudes