Copter: add Y6 with all top props CW

Set FRAME parameter to 10
Copter: pre arm mag offset limit to 600 for PX4
Copter: update THR_MAX @Range and comments
Merge remote-tracking branch 'remotes/ardupilot/master'
Copter: increasd default logging for PX4, Pixhawk
TradHeli: bug fix for main rotor ramp up

The main rotor ramp was being held back by the rotor speed estimate
instead of being allowed to jump up to the estimate if it's lower.

Also fixed some incorrect indentation
Copter: remove AN0~AN15 pin definitions
Camera: correct _trigger_type comment
Copter: log flight mode to dataflash on start-up
Copter: ignore yaw input during radio failsafe
web: added icon for SiK firmware
web: fixed icon
Copter: reduce autotune min rate P to 0.01 (was 0.02)
GPSGlitch: reduce radius to 2m
Copter: AC3.1-rc8 release notes
Copter: reduce autotune min rate D to 0.002
AP_InertialSensor: added support for multiple accel/gyro devices

this makes it possible to ask for the gyro and accel vectors from
secondary INS devices.
AP_InertialSensor: implement up to two sensors on PX4
DataFlash: added Log_Write_IMU2() for logging 2nd INS sensors
PX4: start all sensor types on PX4

this allows for secondary sensors