OR-734 augment communitiesController#join : a user can join a community if he had been invited into the community
OR-734 unit-tests
OR-734 midway tests
Merge pull request #515 in OR/rse from OR/rse-gcrosmarie:OR-734-Augment-PUT-api/communities/communityId/members/userId to master

* commit '6fa71b3809a881888c11e7dc0afcddca4d49ece4':
  OR-734 midway tests
  OR-734 unit-tests
  OR-734 augment communitiesController#join : a user can join a community if he had been invited into the community