Query function for throttles. (#461)
Query function for throttles. (#461)

The query function allows the throttle to request the current function state from the remote (train).
Adds query_fn to the Throttle interface.
Fixes todo to invoke client callback when a function state response arrives.
bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn,bakerstu/openmrn