BUG 2805 - Fixed Restconf RPC calls and POST to create data

RPCs now works again with JSON and XML
POST works with data store.

AbstractIdentifierAwareJaxRsProvider and its derivates,
provides InstanceIdentifierContext as was parsed from
RESTCONF URI, along with parsed NormalizedNode.

If operation is create, then parsed NormalizedNode
is used along with InstanceIdentifier context to compute
full InstanceIdentifier for data to be created
and works with these data.

This actually simplified flow in codecs.

Change-Id: I5b12965f35d946087cc57f19a28425b27eb27755
Signed-off-by: Vaclav Demcak <vdemcak@cisco.com>
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>