Copter: initialise waypoint leash length

Without this initialisation the first RTL could be too aggressive as it
tries to stop too suddenly
Copter: add OctaQuad V frame
Copter: reduce default logging for SITL
PX4: change FMUv2 bootloader USB ID to 0x0011
PX4: added automatic IO firmware update

this avoids the px4io.loaded file on the SD card that confused many
users
AP_InertialSensor: prevent INS healthy errors while initialising

during gyro cal we shouldn't mark the gyro unhealthy
AC_WPNav: reduce leash length for stopping

We now limit the target stopping point to 1x the xy leash length while
previously it was 2x.  This is justified because this limit is only used
when the copter is travelling at higher speeds but at higher speeds air
drag tends to make the copter stop more quickly naturally.
DataFlash: don't try to create a directory that exists

this is an attempt to avoid microSD card corruption. The most common
corruption is two 'logs' directories, which may indicate an issue with
trying to create it a 2nd time.
AP_InertialSensor: another attempt at fixing the spurious bad gyro health warnings

cope with _get_sample() not being called for a while
Copter: 3.1 release notes
Copter: remove unnecessary MPU6K filter definition

This should also help kick off the AC3.1 rebuild
TradHeli: Fix for yaw offset switching.  Yaw Offset should switch on and off with the main motor, not waiting until the rotor has reached full speed.
RC_Channel: improved docs for RCn_FUNCTION=0
Rover: added timestamps to logging and new STER logging

much more accurate logging for better analysis
Test: testing commit

This is a test commit
Copter: removed some unnecessary fields in GCS.h

save some memory
Rover: use common GCS.h
Copter: moved GCS.h to common library
Plane: use common GCS.h
GCS_MAVLink: import new mavlink XML