Upgrade to Jupyter Notebook 4.0

* Change minimal-notebook to install notebook=4.0*
* Change other Dockerfile to point to 4.0 Docker Hub tag (to be built)
* Change config and pem file paths for jupyter
* Install ipywidgets in all containers that have a Python stack
* Update all READMEs to describe v3.2 and v4.0 since Docker Hub only shows one README for all tags

Contribution (c) Copyright IBM Corp. 2015

Add a Gitter chat badge to README.md

Allow notebook patch release to vary

* Noticed that r-notebook was installing ipython 3.2.1 while the base image already had 3.2.0

Contribution (c) Copyright IBM Corp. 2015

* Proper apt-get update for system pkgs
* Bump r-devtools to 1.8 and fix conflicts

Contribution (c) Copyright IBM Corp. 2015

Notebook stack Scala, Python, and R w/ Spark on Mesos

(c) Copyright IBM Corp. 2015

Notebook stack for Python w/ Spark on Mesos

Plus README explaining how to use pyspark in local mode and with a
Mesos cluster.

(c) Copyright IBM Corp. 2015

Make NotebookApp.ip and .port configurable

Necessary when running Docker with --net=host to avoid unknown port jumps and exposure on all host interfaces

(c) Copyright IBM Corp. 2015

Initial stacks