Versioned Release Plugins rather than master

[ajlennon]

We should probably move the Docker build to specific versioned releases of plugins rather than just using whatever happens to be in master whenever a build occurs

[MatthewCroughan]

https://github.com/jitsi/docker-jitsi-meet

This project does Docker-centric versioning right. The master repo contains nothing but :latest for everything. But they release tarballs, which just simply pin everything to a version.

[ajlennon]

It's easy to change master.zip to the correct versioned releases. I just need to do it :)