Add support for BinderHub

As an addition to our support for JupyterHub, we should consider support for BinderHub as well. BinderHub works alongside JupyterHub, and is able to build notebooks on demand to provide customized computing environments, built from a Git repo.

This would allow us to have a clean way to integrate notebooks that are different than the base notebook, as people frequently need to manage their dependencies. (Or have a very large notebook with many dependencies, which then takes a long time to launch.)

• BinderHub: https://binderhub.readthedocs.io/en/latest/
• GitLab Support: https://github.com/jupyterhub/binderhub/pull/266/files
• repo2docker: http://repo2docker.readthedocs.io/en/latest/