Allow user to specify different score thresholds for different taxa #233
Description
Currently, deconv only allows the user to specify a single score threshold (-t [ --threshold ] arg), which is applied identically to all taxa. However, because some viruses have larger genomes than others, and the number of peptides included in a design for each species may be quite different, it would be useful to be able to set score thresholds that are different for different taxa (i.e., TaxIDs in linkage map).
As a starting place, let's allow users to provide a tab-delimited file (in place of an integer) to the "-t" argument. This file should contain two columns: 1) TaxID (one row per TaxID) and 2) the score threshold to use for that TaxID.