Some contributor documentation

Don't chown -R a user's home directory

If people have a use case for recursive chowns that's fine.  I think it's dangerous for people to use, but that's tailored to my use case.

My attempt at reorganization

Made language stronger on this for variety.

extraneous space removed

Took out bullets and reworked item 3

Trimmed line 2 for clarity and moved sections and added headings

CHOWN_EXTRA is a comma separated list of directories to chown.

send2trash not work

https://github.com/jupyter/notebook/issues/3130
Now, files not delete on https://hub.docker.com/r/jupyter/base-notebook/ and derived container images.

Only the top level permissions are set wrong due to kubernetes not being able to do this automatically.

This hits significant problems when the chown takes more than 30s and the pod fails to start

Update scipy-notebook packages

Update tensorflow to 1.5, keras to 2.1

Added missing conda clean to pyspark-notebook Dockerfile

Update miniconda installer to 4.4

Update scikit libraries

Release notes can be found here https://github.com/scikit-image/scikit-image/blob/master/doc/release/release_0.13.rst

Release notes can be found here http://scikit-learn.org/stable/whats_new.html#version-0-19-1

Update toree to rc5

Update jupyterlab and extensions

Update jupyterlab from 0.31 to 0.32.

Update the following extensions to matching versions:
- jupyterlab/hub-extension
- jupyter-widget/jupyterlab-manager
- jupyterlab_bokeh

Force npm cache clean

Remove facets directory

The `cd` command switches to the user's home directory (away from the directory we want to delete)
Then we remove the facets directory using the full path

In start.sh ensure usename jovyan exists before attempting usermod