Have AssignGenes pass igblast warnings to the user somehow

[Jason Vander Heiden]

We should capture error/warning messages from igblast in AssignGenes and pass them to the user. Dumping them to the console ends up being prohibitively ugly (any non-ACGT character results in a message). Maybe via a --log argument? Or a separate output file that olds the igblast error log?

See #179.