DOMDataTree APIs

DOMDataTree APIs

This patch introduces the end-user visible API model for interacting
with the conceptual data tree. Unlike our previous APIs, these revolve
around applications explicitly binding their inputs (former data change
listeners) and outputs (former explicit writes). This allows efficient
inter-datastore interactions to be maintained by understanding what
sort of output applications make and what sort of indexes are required
to feed them the data they require. Beryllium evolution will see the
DOMDataTreeListener being subscribed to an XQuery expression, thus
providing a dense definition of what data the applciation actually
extracts out of the subtree.

Change-Id: I11446ce7f8dbd7cf61540f72e463460b483ff15f
Signed-off-by: Robert Varga <rovarga@cisco.com>