Implement room address suggestion
Implement room address suggestion

Rooms of the same building, especially one that'? about to be created,
usually have the same address data (except for `addition`).

Not providing the user this preexisting data would be inefficient.

Refs #334

agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft