This gives much better information to the UI layer, getting rid of a
whole troubleshooting guide entry. See #119#132#218#219
I also restructured the code in anticipation of a new WebSocket event
stream (#40).
This fixes a real cross-site WebSocket hijacking (CSWSH) vulnerability.
If the attacker knows the URL of an NVR installation this user is
authenticated to and the UUID of a camera, and can trick the user into
visiting their webpage, they can grab the live stream. At least there's
some entropy in the camera UUID, but it was never intended to be a
secret.
