MAINT: remove `rank` deprecation warning

This was being raised in PyCogent. Update code to use scikit-bio/scipy.
BUG: make_otu_heatmap.py now makes room for long axis labels
ENH: add --width/--height to make_otu_heatmap.py
ENH: add --dpi and --imagetype to make_otu_heatmap.py
DOC: update outdated plot_heatmap docstring
Merge pull request #1767 from jairideout/even-more-quick-fixes

improvements to make_otu_heatmap.py