Better error handling (and a bugfix)

Error handling

If a websocket connection dies a loud error will be shown to the user like this:

If any uncaught exceptions happen (e.g. can't connect to the server, js errors or otherwise) you will see an error page like this

This is not 100% perfect, but way better than the current state where nothing is shown to the user, and zero effort to recover is done.

Bug fix

Previously broadcasting of updates to jobs, allocations, evaluations and other lists in the system was only sent to one websocket, now its correctly sent to all connections subscribed to the same resource :)