the EntryCollector instance associated with a given workspace is listening to any modifications made to the access control content
(add, modification and removal of access control lists). however, due to the structure of the ac content (the ac node being attached to the affected nodes)
caches may become stale if a node is moved that contains ac information somewhere in the subtree.
in order to circumvent that problem the EntryCollector should in addition collect any kind of move operations
and make sure that the caches are updated accordingly.