Use direct getters for Tdc as well + some renaming

- Instead of having to call the mot_req_XXX method
followed by a get_XXX method, now one only has to call mot_get_XXX
which will send the REQ message and wait for the answer (GET message)
and will return back the requested value(s) (either a single value or a tuple).

- msg_get is renamed as get_msg