New content notification performance improvements
Fix performance regression introduced when fixing websocket pushes.
When ensuring websocket pushes are always delivered to the right participants, for every stream, which happened by moving the sending to the background workers from the signals, I also made Socialhome horribly inefficient especially for sites with more users.
Now we only notify users who have actually been recently online, based on websocket stream activity. Attempts are made to skip doing expensive database lookups on whether or not to cache/notify something if no caching or notifying is going to happen.
Also try to re-use existing Redis connections instead of constantly creating new connections.