Multi-camera streams in the client user interface

[curtiswest]

With the addition of multi-camera servers in v3.0 comes the ability to stream from these multi-camera servers.

The present implementation of the user interface only displays one of these streams (the first in the streams_url reply from the server).

Ideally, there would be a way to display all of the cameras connected to a server in that servers panel. This shouldn't require any backend work -- after all, the stream URLs are already being accessed, but they're discarded before being used. Implementation will require modifying the Flask templates setup.html to display these streams.