prepend R channel

bump jupyterlab and install jupyter-labhub extension

avoids broken R due to mismatched icu version (probably a bad or missing pin somewhere)

Patch R package install user issues

-The following patch addresses issue #489
(https://github.com/jupyter/docker-stacks/issues/489)

bump miniconda version to 4.3.30

MAINTAINER is deprecated, using LABEL now

Update jupyterlab to 0.28

Upgrade to notebook 5.2.0

Update jupyterlab from 0.27.* to 0.28.*. This allows the current
version of ipywidgets (7.0.2) to be installed.

bump jupyterhub to version 0.8

Upgrade to notebook 5.1

Fix facets install

* Don't change WORKDIR
* Fix permissions after install
* Cleanup source tree

Added support for facets visualization

Further emphasize the use of tags in README

homedir fixes

- don't relocate home if home exists (e.g. mounted volume)
- respect workdir, only cd to new home if we were in /home/jovyan/

Fix working directory problems with custom NB_USER

Fix inherit-diagram: debian@SHA -> ubuntu@SHA

Based on https://github.com/jupyter/docker-stacks/pull/428/commits/0351f0c3b7743026e2aec161b8e23a4182408c74

Add keras

Improve start.sh logging along the way

Update ipywidgets to 7.0.x

[ci skip] Remove py2 reference