Ins stability improvements

Since Qt5 is stalling so long and this originally depended on it, I cherry-picked #448 down to next.  This is a rework on the attitude module to support running the complimentary filter and the EKF simultaneously (e.g. fly with CF but use EKF for navigation, or use raw for navigation).

In addition there are some changes to how the EKF initializes and behaves which helped substantially.

I've been flying this quite heavily for a few months so feel confident in it.