Add hierarchical clustering tool using Christopher DeBoever's script

Hierarchical clustering tool based on script here:
http://nbviewer.ipython.org/github/ucsd-scientific-python/user-group/blob/master/presentations/20131016/hierarchical_clustering_heatmaps_gridspec.ipynb

Licensed under MIT
Hierarchical clustering fixes/improvements
Merge branch 'master' of github.com:pathomx/pathomx