Switch the default port in docker-compose from 5000

[jonespm]

It seems like port 5000 is used by Apple Airplay Receiver. This can be disabled in Settings->General (18.1) to free this port up but would be fine to just pick a different default port for this. Maybe just change it to 8000 or similar which is the Django default. This might conflict with some of our other apps. I'm not sure if it's worth picking different ones for each app?