Actuator: handle devices without limits (no actuator_state_in and actuator_state_out)

@sallazda has devices (like fluo lamps) without limits (no actuator_state_in and actuator_state_out).

Such devices could be handled with a few changes to the current Actuator class.

Basically when there is no key_in or key_out, the state is assumed by the key_cmd.