Initial implementation of netconf monitoring module according to http://tools.ietf...

Response from netconf GET operation now contains monitoring information about current netconf state.

Modified netconf-impl module: added monitoring capabilities to netconf-impl module exposed as OSGi service.

Added netconf-monitoring module that provides a filter for netconf GET operation
and adds monitoring information retrieved from netconf-impl to the response of the GET operation.
It implements netconf-mapping-api similar to config-netconf-connector and
currently provides information about current netconf SESSIONS and yang SCHEMAS
(these information is retrieved via the netconf monitoring OSGi service provided by netconf-impl).

Added ietf-netconf-monitoring module that contains sources generated from ietf-netconf-monitoring yang.
These sources serve as an interface between netconf-impl and netconf-monitoring.

Change-Id: I62c457cde42e01781d9039c6dde0a03115134df4
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>