AP_InertialSensor: allow gyro calibration to take up to 30 seconds

this gives time for the user time to get their battery hatches on and
hold the model steady. 5 seconds was just far too short
AP_NavEKF: add another health check in the EKF

if SV, SP and SH are all off then the most likely cause is divergence
of the EKF. This was done based on a flight log with bad gyro cal
Replay: cope with new airspeed log msg
AP_NavEKF: added getStaticMode() function
DataFlash: added staticmode to EKF4 message

useful when diagnosing logs