Dockerfile version for power ppc64le

adding a patch file to make Dockerfile.ppc64le more maintainable and updating the Makefile to make use of the patch file

JupyterHub 0.7

and get it from conda (conda-forge)

single-user protocol should still be compatible, so this shouldn't change supported Hub versions

Add vincent, beautifulsoup, and xlrd to scipy-notebook

Update Julia version to 0.5

This is pretty hacky -- we're using a Ubuntu 14.04 PPA to install
something on Debian Jessie -- but everything seems to work.

Add badges with image size and layers

This uses the MicroBadger badge service. It allows prospective image users to
quickly get an idea of the size of an image from glancing at the README.

Don't mix mkl and open_blas packages

* Bump numexpr to 2.6 so it comes from conda-forge
* Install nomkl

Update pandas to version 0.19*

Fix #269, NB_UID regression

Version 0.6 does not work after all containers rebuild

Workaround docker / aufs permission problems

Convert readthedocs links for their .org -> .io migration for hosted projects

As per [their blog post of the 27th April](https://blog.readthedocs.com/securing-subdomains/) ‘Securing subdomains’:

> Starting today, Read the Docs will start hosting projects from subdomains on the domain readthedocs.io, instead of on readthedocs.org. This change addresses some security concerns around site cookies while hosting user generated data on the same domain as our dashboard.

Test Plan: Manually visited all the links I’ve modified.

use cdn for apt

Build matplotlib font cache during docker build.

httpredir fails semi-regularly

Update ipywidgets to 5.2