Add a Dockerfile with pre-setup configuration

[lagergren]

In the interest of making it as easy as possible to get started and get all configuration right for XTC, so that you can literally just install and run "hello world", we should add a Dockerfile, so that the user can build and deploy xtc containers with some trivial stuff in them. We should also push an xtc master image to public docker repositories so the user can build and run xtc programs in a working environment without having to clone and build any source.

Finally, we should verify and make sure dev container approaches work for a dev environment for XTC. Dev containers integrate well with most IDEs, e.g. VS Code and IntelliJ, and they both have built in mechanisms for using existing Dockerfiles to form them, I think.