Persistance of position relocations moved to other events to fix issue #1209

[leonex-cs1]

This PR fixes issue #1209. Please refer this issue to understand the background of this patch.

• I have added an unit test for issue [Sortable] Positions are updated on entity remove, even if removing failed #1209
• Moved the persistance of position relocations from onFlush event, which is called before database transaction started, to the first call of postPersist, preUpdate or preRemove. So that the update query is executed within the transaction and if errors happen during queries the position changes will be rolled back.
• The synchronization of the objects has been separated from the database persistance, so that it will happen only if all queries were successfully executed (in postFlush).

The only thing I don't like with this solution is, that it will only work with entities that have identifiers. I am not sure if this is a problem.
I had to use these because the INSERTs are executed before the UPDATE query for the relocation of the positions. And that will manipulate the positions of inserted records. But I cannot use another event in this case.

Doctrine lacks an event which is fired between the beginning of a transaction and the inserts :-( This would have made the patch much simpler.

[leonex-cs1]

Testing on a live system showed that the shouldSyncPositionAfterDelete did not test if the positions have been persisted correctly. So I have extended the test in 79544ff.

Further I had to move the call to relocation persistance from preRemove to the postRemove event, because preRemove is executed right after calling $em->remove($entity) and not in flush.

I hope it's okay, that I have done that in multiple commits.

[l3pp4rd]

thanks, that was very useful