more conversion stuff

some fixes and added area unit drop down

Conflicts:
	src/MissionEditor/MissionItemStatus.qml

removed comment

finish unit conversion

correcting typos

Use constant's inverse to ensure we don't accumulate error when converting back and forth

Use constant's inverse to ensure we don't accumulate error when converting back and forth

 - Request list of all parameters, expecting device to lead each component with _HASH_CHECK cache value
 - Test for hash collision, if so our cache is valid and respond with _HASH_CHECK to stop listing
 - Else: let listing continue as normal to get updated param values
 - Store each cache by systemID + componentID

For #2586

Plumb through initial object mode on Vehicle

Allows parameter access from QML among other things

Used for unit testing