Copter: added AUX switch option for enable/disable EKF
AP_AHRS: added set_ekf_use()
Copter: use GPS AIRBORNE_4G
AP_AHRS: use the right DCM matrix when EKF not enabled
AP_NavEKF: copter specific dtIMUAvg
AP_NavEKF: use INS delta_time
AP_Math: make to_euler() const
AP_AHRS: fill in _dcm_matrix whenever EKF started

this ensures get_dcm_matrix() always returns valid data
AP_AHRS: start EKF 5 seconds after getting GPS lock
SITL: prevent initialisation error
SITL: use sinf() and cosf()

for some strange reason the double precision functions can crash
AP_NavEKF: tweak parameters based on randys copter log
AP_NavEKF: added PositionReset public function to fix pre-arm loss of solution
AP_NavEKF: added static mode for pre-arm and bench testing
AP_NavEKF: reduced On Ground yaw gyro bias drift variance scaler
AP_NavEKF: Misc tuning adjustments for Plane testing
AP_NavEKF: changed GPS fusion mode back to 0 for further plane testing