Fix unittests in python3.3 and python2.7

This is a branch which tries to fix all unittests under py3.3 and afterwards py2.7 and the old matplotlob version. 

Current status:
* [x] faceting will produce different ylims in some cases under py3.3
* [x] Fix for overploting the upper row of a faceted plot with the complete data
* [x] Unittests under py2.7
* [x] Unittests under py3.3
* [x] Unicode fixes and other stuff (#167 -> "Add all the `from future...` imports...")
* [x] install brewer2mpl in travis