[TASK] No persisting in event indexer

The persisting was removed from the destructor in the event indexer
because it could cause errors when the database connection was not
available any more.
[TASK] Rewritten event index deletion

The deletion of event index entries is now also handled by an extbase
repository so that the reference index entries stay clean and valid.
[TASK] Rewritten data handler hook

The data handler hook was completely rewritten.

The command map and data map hooks have been consolidated in one hook
class.

To prevent duplicate indexing calls all changed events are collected
first and at the end of the processing the index for these events is
updated.

Since the event indexer does not persist any more at the end of all
operations the persistence manager is called to persist everything.

Some duplicate code was removed and the deprecated class names have
been replaced with namespaced versions.