https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_17193335

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_17146325

At the moment we cannot see weather a user left a project due to their
membership expiring of if they themselves opted to leave the project.
This adds a new event type that allows us to make this differentiation.
Note that is not really feasable to go back and reliably fix up the
previous events. As a result the events for previous expire removals
will remain the same however events of this nature going forward will be
correctly represented.

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fixed all related specs and also changed the logic to handle edge cases. This includes exporting and exporting of group labels, which will get associated with the new group (if any) or they will become normal project labels otherwise.

Found other issues to do with not being able to import all labels at once in the beginning of the JSON - code was much simpler when we import all labels and milestones associated to a project first, then the associations will find the already created labels instead of creating them from the associations themselves.