JCR-2113: Writing access control

This patch addresses the following as indicated in https://issues.apache.org/jira/browse/JCR-2113:
a. adjust jcr2dav module and make sure the RepositoryConfig gets a valid ac-provider configuration parameter set
b. complete setPolicy, Batch#setTree, + testing
c. complete removePolicy for jcr2spi and complete implementation for removal of protected items on jcr-server.

i just played around with it and found that using the operations might not be that straight forward as it doesn't reflect the hierarchy directly... but if we had SetTree#getTreeState would offer the root of that tree that would then been used to traverser the subtree and add the child items to the Tree... let me try if that works.