Updated Docker image

Hi, thanks for forking my project; I'm just starting out coding and it's really encouraging to have this happen to me. The version you forked was really hacky; this is much more thorough. Also, if the Etherpad devs are interested in giving this some sort of official curation, would you be interested in setting up an account at index.docker.io which would be a trusted build linked to your Github repository? Right now I have the readme suggesting that anyone interested pull an image from my account, which may be weird.

Thanks again,
John