Use certbot from Ubuntu repo (ref #45)

Lets Encrypt certs were breaking on the production server, so I rewrote our certbot script. The problem there was this one, I guess we messed up something in the certbot config during one change or another.

I already tested first run and cert renewal, this script version is also running on ecloud.global. We might consider #45 fixed with this patch, because its probably the simplest option we can use. Advantages over the old setup (with certbot-docker image):

• certbot from ubuntu repo should be more stable and well-tested
• less complexity (no need to mount different volumes)
• less docker images (but on the other hand, we need to install a bunch of python)
• certbot updates are handled by apt