* pr-ekfOptFlowFixes:
EKF: fix bug causing height offset when GPS use stops
EKF: Don't reject saturated flow data when it is the only aiding source
EKF: Prevent flow motion check false positives
EKF: Don't assume large position uncertainty when starting optical flow nav
EKF: relax terrain update requirements for continuing optical flow use
EKF: Relax minimum required range finder measurement rate
EKF: relax optical flow on ground motion checks
EKF: range finder aiding logic fixes
EKF: Decouple range finder use criteria checking and selection
EKF: Don't auto select range finder for height when on ground.
EKF: Fix false triggering of optical flow bad motion checks
EKF: update comments
EKF: Don't use optical flow if GPS is good and the vehicle is not using range finder for height
EKF: Stop using EV for yaw when GPS fusion starts
EKF: Add persistence criteria to GPS fail check
EKF: allow GPS fallback if quality bad and alternative aiding available
EKF: always run GPS checks
Remove duplicate checking for dead reckoning and consolidate into a single function.
Use separate timers to check for start of dead reckoning and check when dead reckoning has been performed for too long for the nav solution to be valid.
Allow the timeout for validity reporting to be adjusted externally.
Separate external reporting of dead reckoning from internal checks.
* EKF: Move optical flow specific state reset to helper functions
* EKF: Ensure loss of optical flow aiding is handled correctly
If data is only source of aiding and has been rejected for too long - reset using flow data as a velocity reference.
If flow data is unavailable for too long - declare optical flow use stopped.
Use consistent time periods for all resets
* EKF: Ensure loss of external vision aiding is handled correctly
If data is only source of aiding and has been rejected for too long - reset using data as a position.
Don't reset velocity if there is another source of aiding constraining it.
If data is unavailable for too long, declare external vision use stopped.
Use consistent time periods for all resets.
* EKF: Update parameter documentation
Make the distinction between the no_gps_timeout_max and no_aid_timeout_max parameters clearer
* EKF: make class variable units consistent with documentation
* EKF: Don't reset states when optical flow use commences if using external vision
* EKF: Stop optical flow fusion when on ground if excessive movement is detected.
* EKF: fix terrain estimator vulnerabilities
Reset estimate to sensor value if rejected for 10 seconds
Protect against user motion when on ground.
Fix unnecessary duplication of terrain validity check and separate validity update and reporting.
* EKF: remove unnecessary Info console prints
Optical flow use information can be obtained from the estimator_status.control_mode_flags message
* EKF: fix inaccurate comment
* EKF: remove duplicate calculation from terrain validity accessor function
