Fixed TILT_STOP command issuing chain that was causing a running channel
to be stopped when an opposite direction tilting requested. For exeample:
RUN_FORWARD > TILT_REVERSE. Refs #1105 and fixes #1110.
Added a state to string public API function. There was already
a private function (`relay_chn_state_str`) that provides
this functionality. So this function has been renamed to
`relay_chn_state_to_str` and made publicly available.
Refs #1104, #1105 and closes #1108.