AP_NavEKF: Add ability to inhibit in-flight mag cal and clean up moding

This will enable in-flight magnetometer calibration to be inhibited unconditionally,
This is required for long balloon carriage flights where ground speed can be high
enough to put it into in-air state, but with very poor observability of magnetic field
states causing bad state estimates and heading offsets to develop over time.

Also adds a filter divergence check that will declare the filter unhealthy if
position, velocity and magnetic field observations are all failing their innovation
consistency checks. This unhealthy status will persist for 10 seconds after the
condition clears.
AP_NavEKF: Use baro data during launch transients whilst in static mode

Baro data can be used as it will still be valid during the launch and
is not a synthesised measurement.