CORE-4666 Cleanup handler in ManageCollaboratorsPresenter.

Added a ManageCollaboratorsView#Presenter#cleanup method.
Updated ManageCollaboratorsPresenter to remove the UserSearchResultSelectedEventHandler from the EventBus in its cleanup method.
Updated ManageCollaboratorsDailog to call this cleanup method in its onHide method.
Merge branch 'master' into data-svc-caching