improve secure_path modification by storing in sudoers.d

Ensure directories/files under home directory are writable.

Templates for deploying Jupyter Notebooks to OpenShift.

Use NB_UID for USER statement in Dockerfile so deployment platform can verify that image doesn't run as root.

Use NB_UID for USER statement in Dockerfile so deployment platform can verify that image doesn't run as root.

Upgrade to the first JupyterLab beta v0.31

Fixing PYTHONPATH in base-notebook/start.sh

jupyterhub-lab support will be enabled if $JUPYTER_ENABLE_LAB is set.

Support provisioned storage with incorrect permissions

I ran into an issue when trying to get this to work with a NFS server which I did not have direct control over (EFS).  As part of the PersistentVolumeClaim, there is no easy way to set the UID and GID of the created directory.on the networked FS.

My only concern with this chown is that some user out there might be running jupyterhub in an odd configuration where $NB_USER is not supposed to have these exact permissions on the storage.  I think this is quite unlikely, but it is worth mentioning. 

I chronicled my experiences with working around this issue and setting up z2jh on EFS in https://github.com/jupyterhub/zero-to-jupyterhub-k8s/issues/421 with @yuvipanda.

Add /bin to sudo secure_path

Update Dockerfile to install r-hexbin

Fixes #532

Append /opt/conda/bin to the sudo secure_path

Retain behavior when su was used instead

 Fix for granting SUDO to jovyan user and run bash commands.

* Refactor to use sudo to become jovyna when the
  container starts as root
* Retain all environment variables when becoming
  jovyan
* Handle start.sh without additional commands when
  launching a container as NB_USER too