GatewayConnection: unify & improve logging of messages
GatewayConnection: unify & improve logging of messages

Messages are logged as trace with details and as debug with
a short note about the message. There now always only one
log per message at this stage (before, there could be more
log records).

Signed-off-by: Jan Viktorin <3eab6ac54c005c4408f608556a6663b7f2abede7@fit.vutbr.cz>

BeeeOn/server,BeeeOn/server,BeeeOn/server,BeeeOn/server