GPS-enabled modes working, ALT HOLD working

GPS modes now work if parameters are set correctly,
ALT HOLD does not go crazy with EKF anymore.

Erle Robotics v1.0

Erle Robotics v1.0 snappy

HAL_Linux: Select MPU9255 by default

Select MPU6000 by default

Select MPU6000 by default

HAL_Linux: Add instructions on how to set up autoinit

Plane: prepare for 2.78b release

Plane: prepare for 2.78b release

Copter: firmware to AC3.1.2-rc1