Plane: use common EKF logging
Copter: enabled EKF and SIMSTATE flash logging
AP_NavEKF: improved covariance matrix numerical stability protection
AP_NavEKF: explicitly zeroed covariance matrix priro to setting initial values
AP_NavEKF: updated timeout for GPS retry and reduced onGround gyro bias noise multiplier
SITL: fixed SIM df altitude
SITL: fixed PX4 build
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_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
HAL_Linux: fixed stopped clock delay
AP_NavEKF: fixed log playback for copter