Setup Teaspoon + Mocha for frontend testing

I've been finding that Capybara + Rspec are woefully unsuited for dealing with Ember (and they're also slow as heck). I think we'd be better served by having some legit JS tests, from unit tests all the way up to feature tests. (The only downside of this approach is that I think we're going to have to use some sort of fixtures or a mock server like https://github.com/trek/pretender instead of the real server.)

This just sets everything up so we can use Mocha. Feel free to pull this down and poke around before merging. To run the tests in the command line, you can do `rake teaspoon`. (I've added this command to the Travis config, as well.) To see a nice report in the browser, you can go to `localhost:3000/teaspoon/default`.