Fixed race issues in config upload, tested to be reliable now - board startup scripts now need the other half of testing

Instantiate a PX4 config view in PX4 mode from start, since boards with just the bootloader (or no working telemetry) cannot be flashed else.

don't process updates to unmapped rc channels when we're not in
calibration mode

Minor improvements in airframe config, param transfer / reboot are still not quite doing what we want

- minor refactor of airframeconfig.cc
- add placeholder for new scratch build multirotor

Add "skip" buttons in msg box (instead of cancel); allow user to cancel
upload of rc params after reviewing them