Add Test Dependencies to setup.py

[pathunstrom]

Didn't realize I hadn't done this, we should absolutely have the setup.py set up to manage test dependencies.

[AstraLuma]

To be fair, very few projects do this.

[nbraud]

@pathunstrom I'd rather have them in an easily-parsed form, and have setup.py read it out, as I did in nbraud@5eb0550. That way, it's easy to get the list of dependencies when building a test environment.

I guess this is in reaction to commit 05e61a6 in #220 ?