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

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

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

still some remaining issues with pending line items bouncing back from
data model

fix pending items indicator