- 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

Add persistRcValuesButt to allow mappings to be persisted outside the
calibration mode; cleanup const params in param dataq model;  add some
debug for mapping problems

Checkpoint: RC calibration much better / operation, can use UI tweaks. Airframe config in, but not operational and still very functional / ugly.

when param widget is loaded we only want to re-request the whole param list if we don't already have one