Flesh out MakeDb unit tests

[Jason Vander Heiden]

We've made a lot of changes to MakeDb recently, and I think we need to decent suite of unit tests in place for MakeDb to test that the imgt, igblast and ihmm subcommands all behave consistently with the various flags.

Should include tests for IgBLAST v1.4, v1.5 and v1.6, IMGT output in old zip format or new txz format, and both B cell heavy/light and T cell beta/alpha chains.

There are a few more issues that we should probably cleanup before running in through rigorously. Particularly issues #81 and #85.

[Jason Vander Heiden]

As of ae229b4, MakeDb-igblast is in a state that could be properly unit tested. Though, ideally, readIgBlast should be converted to a class.

[Jason Vander Heiden]

Converted the igblast parsing operations to the class IgBlastReader in dbccd91, which will return either a dict or IgRecord. Should make testing a lot easier.