split apart dependencies of vaccine peptide selection

* added unit tests for individual ranking components
* vaccine peptide sorting by four criteria (mutant epitope score, negative wildtype epitope score, number mutated residues, distance of mutation start the edge of vaccine peptide)
* print and write FASTA of vaccine peptides with a little mutation metadata
* print epitopes associated with each mutation
Ah: "The default selection IEDB Recommended is provided. Based on availability of predictors and previously observed predictive performance, this selection tries to use the best possible method for a given MHC molecule."

Why did you switch to this?