Reaction network updates

[semiller10]

A reason for this PR, which will not close out the branch, is to make sure that a profile database migration script to v40 is put into master before other developers create such a script doing something else :p

Here are major additions in the PR.

• Pangenomic reaction network functionality is brought up to speed with (meta)genomic reaction networks.
• "Subsetting" methods to extract subnetworks from reaction networks are added. For instance, one can extract the subnetwork of a genomic network involved in the metabolism of a list of metabolites of interest, or a subnetwork involving certain genes of interest.
• A new class for testing reaction network functionality -- I hesitate to call this unit testing, because it is not that granular, but it is relatively comprehensive.
• Protein and metabolite abundance profiles (i.e., from proteomics and metabolomics) can be imported in tab-delimited tables to be stored in profile databases and hence loaded into genomic networks, integrating proteomics and metabolomics with genome-resolved metabolic networks.

[meren]

Holy PR :) anvi-import-metabolite-profile and anvi-import-protein-profile sound like poetry.