Better handling for Repository Messages

Depending on the way the core API is used, creating a document can result in several Messages (Created/Modified).
When theses messages are used to trigger sync or async indexing they create unuseful load : like indexing twice the same document.
This is particularly bad when triggering async processing that are done in seperated thread : it creates deadlocks.

We should clean up a little this part :

• drop sync indexing messages when DM is not populated
• make duplicated messages as duplicated and let listener service choose if the message needs to be processed
  => the search service does not need to process 2 indexing event on the same doc in the same transaction
  => audit service may choose to log all events