BVS-682: Service insertion changes in quantum/bigdashboard

On AddRouterRule form: 1) enable nexthops field, 2) make source/destination
a drop-down menu plus an IP/CIDR field.
Merge branch 'grizzly/router_rules' of https://github.com/bigswitch/horizon into bvs-682

Conflicts:
	openstack_dashboard/dashboards/project/routers/extensions/routerrules/forms.py