Show app version in "footer"

[xy2z]

When the Docker image is built, it should get the current git tag as an env variable, so in the code we can show what the current version is.

This probably means the Dockerfile should install git, get the latest/current tag, and uninstall/purge git after that.

I was hoping Docker would set this env automatically, but apparently it doesn't.

"footer" means below "sign out" link in the left sidebar. Maybe also show it in the login/register/forgot-password pages in the footer.

[xy2z]

This wasn't as easy as I thought...

Docker Hub can't run git commands on build, because it's not a git repository... So I can't do it on the Dockerfile or the entrypoint file. And I don't want to build and push the manually.

I'm waiting till this can be done automated from the git tag (git describe --tags), since I don't want to manually tag every release, and I'll most likely forget.