method on ResidentFacade

preconditions:

• RO is in state PUBLIC
• ROA is in state WAITING FOR INVITATION

actions:

• send mail to seeker with the rejected ROA

post conditions:

• ROA is in state REJECTED

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":77.77777777777777,"status":"backlog"}