Improvements and fixes

Renaming an organization no longer fails when no contact email is stored for it.

• A field cleared in an organization or contact dialog now saves as empty, and an unchanged dialog saves nothing.
• Through the API, /v1/sites now lists the reachable plants without health figures, and /v1/sites/status returns health for the plants named in the call.
• A remote-access route whose subnet contains the reserved address 10.112.0.1 is now flagged, and only that single address stays unreachable inside the plant.