Integrate Cucumber support.

In order to turn the fluffy requirements I have in my head into executable
specifications, I will be attempting to use Cucumber. This particular story is
to get cucumber integrated -- including automatically running the features with
guard, and, on push, with Travis CI. It should be able to test that the home
page is displaying some marketing blurb.

Still a work in progress -- just pushing up the initial pull request to mark
that it's actually in progress.