OR-756 update usernotification middleware according to new model
OR-756 update usernotification pubsub module according to new model
OR-756 update usernotification core module according to new model
OR-756 modify usernotification model : target now is a user id
OR-756 adapt user notifications creation due to new model
OR-756 wsserver now always publishes created user notification to their unique target user
OR-756 update midway test due to new user notification creation behavior
Merge pull request #562 in OR/rse from OR/rse-gcrosmarie:OR-756 to master

* commit '65ab451ad37a0fcd5977508135ab23996693542a':
  OR-756 update midway test due to new user notification creation behavior
  OR-756 wsserver now always publishes created user notification to their unique target user
  OR-756 adapt user notifications creation due to new model
  OR-756 modify usernotification model : target now is a user id
  OR-756 update usernotification core module according to new model
  OR-756 update usernotification pubsub module according to new model
  OR-756 update usernotification middleware according to new model