Paul's Estimator

So this thing is now finally ready for a real pull request. Current state is:

  * Already test flown multiple times
  * Validated on log data in a C-harness
  * Has NaN detection and reset on all states and all relevant update matrices (covariance, Kalman gain)
  * Has symmetry enforcement for relevant matrices
  * Has limits on states
  * Is able to reinitialise on fault in-air, no visible jitter on HUD during re-init
  * Draws 20% load for combined position & attitude estimate @ 200 Hz
  * This PR also adds estimator state logging for post-flight detection of filter resets (logs the state vector on error time as well)

Please help to put *this* exact state through HIL and flight testing. But from my testing it should be ready for prime time by all means, and its the best estimator for fixed wing we ever had.

There are no imminent TODOs, but I'd like to store the logged mag offsets and load them on the next boot. This is great if the inclination and declination were set incorrectly initially.