Indices - add index to calculate richness for each taxonomic level in a data set.

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Having such an index would make it easier to compare richness for family, genus 
and species within a single output.  

Alternately, we could add a flag to run an entire analysis at a higher 
taxonomic level.  This would, however, cause issues with label properties, 
tree, matrices and many of the linked visualisations.  

Original issue reported on code.google.com by shawnlaffan on 23 Mar 2012 at 9:57