otu_category_significance.py replacements

This pull request will remove otu_category_significance.py in favor of two new scripts which extend the functionality while reducing the number of lines substantially. There are at least two tests which will fail when Jenkins tests this in 
make_3d_plots.py and compare_alpha_diversity.py. Both of those tests will be related to no longer being able to import from qiime.otu_category_significance. Once I see what other tests fail (because they imported from there) I will make the necessary changes (I searched, but those are the only two that I actually think will have a problem). Additionally we will solicit new names for the scripts.