Rename files, uffda_client api, add service_event(), service_status()

Did a quick renaming to make things more consistent and easier to understand.
Refactored uffda_client to use a shared function trigger_event and service_event() datatypes.
Added service_status() datatypes, but did not update uffda_service_fsm yet to handle the events being sent to it.
The return value of register_service should be ok, we have decided not to expose the fsm pid to the client.