SLING-3384 Create AbstractSlingRepositoryManager and AbstractSlingRepository2

- Also create new NamespaceMappingSupport base class allowing for better
   integrations going forward
- AbstractSlingRepository and AbstractNamespaceMappingRepository are
   deprecated


git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1566547 13f79535-47bb-0310-9956-ffa450edef68