method on ResidentFacade

Residents can always cancel their RO. The semantics is that there is no longer a vacancy in the flatshare (because they found somebody somehow, or the room is no longer vacant).

preconditions:

• user that cancels must be resident of the flatshare of the room offer

actions:

• display warning in UI if:
  • there are ROAs in states other than WAITING FOR INVITATION
  • special warning if there are ROAs in state ACCEPTED
• send mail to every seeker for whom a ROA exists for this RO
  • sent text is dependent on state of ROA

post conditions:

• Room Offer is in state DELTED and cannot be found anymore

Write test for the pre- and postconditions as well as for the actions.

see https://docs.google.com/drawings/d/1V5rpsgNq0lkfucdDsvnjUf3nhhQ9u1qmP_UXgJliAq4/edit?pli=1
@Gissues:{"order":88.88888888888889,"status":"backlog"}