Docker hub deprecation

[Duncan Ralph]

Docker hub has gradually become unusable (at least on free tier) the last few years, so I am switching to quay.io for docker image building/pulling. The only thing this should change from a user perspective is adding a 'quay.io' to the docker pull/run commands. However, I also need to remove the docker hub repo/image in order to avoid anyone pulling old versions by accident. I'll do this next week, so if you pull from docker hub after that you'll presumably get a 404.