OPENDJ-2349: fix deadlocks during subtree deletes and moddn

The following changes were made:

* ensure that cursors in JE use read committed isolation, not the
default which is repeatable read
* ensure that records are locked in a consistent order during update
operations: dn2id, dn2uri, id2entry, id2childrenCount, and finally the
attribute indexes
* added support for deleting records directly from cursors
* DN2ID: added renameSubtree() method in order to avoid breaking
encapsulation when renaming DN keys during moddn operations
* ID2Count: split apart updates to parent counts and total counts so
that records can be updated in a well defined order. A consequence of
this change is that the total count includes base entries
* ID2Entry: added openCursor() method to facilitate implementation of
subtree deletes and moddn operations.