Add new Dockerfile for only serving static files

[sebastian-aranda]

This PR add a new Dockerfile for serving LOVE-manager static files. The folders with static files are:

• /usr/usr/love/manager/static
• usr/src/love/manager/media

Now the image doesn't run the server, collect static files and only mounts the related volumes.

[mareuter]

I would go one extra step like the frontend does to create a new container that copies out the static files from the build container. That way the static container is smaller and only contains what we need.

[mareuter]

I think that will do nicely. Thanks for making this happen.