Deprecate "extension:xxx" policies but preserve bw compatibility

Blueprint make-authz-orthogonal

Patch #4 for this blueprint.
With this change, if policies starting with 'extension' are still
present in policy.json, a deprecation warning will be emitted, and
the policy will be translated in the corresponding, new-style,
policy(ies).

Change-Id: Iccf0f36cc2547c35c66854b8a3fdb7185b5214bd
Add l3 attribute to network

The fix is to add l3 attribute(s) to the returned objects in get_network() and get_networks()

Fixes: bug #1180971
Change-Id: I4b9c932fae90a169ad1c0119f45e90a2ee260acd
Merge "Deprecate "extension:xxx" policies but preserve bw compatibility"
Merge "Add l3 attribute to network"