Neutron DVR implementation allows to change router type from
centralized to distributed. This commit adds "Edit Router" form
which is not implemented so far to allow this feature.
This commit also adds:
- admin_state field to the router detail.
- documentation on a new option enable_distributed_router
Completes blueprint enhance-horizon-for-dvr
Change-Id: I4b46e44c417726217ed034e305827b102ba656f8