AP_NavEKF: Added VelNED and PosNED to dataflash
Merge branch 'NavEKF-wip' of github.com:priseborough/ardupilot into NavEKF-wip

* 'NavEKF-wip' of github.com:priseborough/ardupilot:
  AP_NavEKF: Added tuning parameter for onGround yaw gyro variance
  AP_NavEKF: Cleaned up on-ground state and covariance update logic