Docker image is misconfigured

[AtkinsSJ]

Carrying on from #350 because this is a different issue than the one originally reported.

I am absolutely not a Docker expert, so I am fumbling my way through this, but from setting up Puter with the recommended Docker Compose installation steps I have a few issues, or possible issues:

1. I couldn't get the regular Docker instructions to work at all.
2. When following the Docker Impose instructions, I had to do a manual chmod 777 on the docker puter directory, otherwise it couldn't start because it failed to write to /var/puter.
3. Once launched, Phoenix doesn't work, as noted in #350. It fails to find its dependencies. This sounds a lot like the issue that was fixed by 4d30753958d6eec27265a3771ebea457042c0f01, but the image does include that change. Manually running npm install from inside the container fixes this, so... somehow we're not running the postinstall. I've confirmed this still occurs with the most recent package.
4. If you look at the packages page, the one tagged latest isn't the latest, it's v2.1.0, and there have been no releases at all for 2 weeks.

[AtkinsSJ]

Looks like issue 3 should have been fixed by #342 but the docker images haven't been built with that. Date wise for me, it was merged on April 24th, and the latest release and latest docker image were on April 23rd.

That docker image claims to be 2.1.1, but maybe the internal version number just didn't get updated?

As a side note, it'd be good if the docker images were named/tagged/whatever to say what release version they are.

[AtkinsSJ]

As far as I can tell, this is completely resolved by #460.