BUG-2633 - Netconf northbound mapping.

Supported operations for now are:
get, get-config - candidate and running datastore, without filtering
edit-config - only on candidate datastore
discard-changes
lock, unlock - supported only for compatibility reasons since we don't support locking of running datastore, and each session has it's own candidate datastore.
commit

Change-Id: Idb0bad09dc1d8925674576290fecb47ccd1e5dbd
Signed-off-by: Tomas Cere <tcere@cisco.com>
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>