Implements a fix for Qt4 and matplotlib by using the new PyQt4 backend in matplotlib (branch)

Previously the Qt5 interface was managed by backend_qt5 a temporary
interface that formed the basis of a complete backend implementation
for matplotlib. This has been commited and a PR submitted for inclusion
in matplotlib v1.4.0.

This is available here:
https://github.com/matplotlib/matplotlib/pull/3072

Clone and install from that repo using `pip install .`
PEP8 fixes