Adds all-in-one Dockerfile for ShareLaTeX installation

This series of commits creates a working Dockerfile which runs all ShareLaTeX components in a single docker container, intended to be useful for development as a lightweight alternative to vagrant. If you want to use docker for production, this might also work, but it would be much more dockery to split each subcomponent out into its own container and tie them together via networking. I may work on that later, but this works as-is. 

I'm not sure you want to merge it as-is, because in order to make the `docker build` not take forever, I've had to split out the TeXLive portion into its own docker image. I currently have this configured as a docker trusted/automated build (`jrandall/texlive` - https://registry.hub.docker.com/u/jrandall/texlive) which builds out of our github repo (https://github.com/wtsi-hgi/docker-texlive). Note that I also have a trusted build `jrandall/sharelatex` for the full sharelatex all-in-one container described here, but which also builds out of our github repo (https://github.com/wtsi-hgi/sharelatex). 

You may want to create a `sharelatex` docker registry account and configure trusted builds to build directly out of https://github.com/sharelatex/ repositories. 

Cheers,

Josh.