Created tests for Invite and InviteController
Added some more funtionality that was still missing for the correct accepting/rejecting/... of invites
Added some functionality for the withdrawing and resending of invites
Fixed the sending invitations from a person to a group
Finished up the last parts of the invite system and wrote changed the tests accordingly
Fixed some rebase errors
Added some comments to clarify a method
Merge pull request #28 from florisverburg/feature_invite_controller_tests

Feature invite controller tests