CAY-1883 - Clean up Cayenne maven structure - get rid of aggregate modules

* moving cayenne-di-unpublished  to cayenne-di and one level up... it is 'published' now

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1542482 13f79535-47bb-0310-9956-ffa450edef68