Add Travis configuration
Mark incomplete scenarios with @wip tag

Otherwise they'll run on Travis, and the build will be marked as
failing (undefined steps count as failures).
Exclude jazz_hands gem from Travis build

All the dependencies of jazz_hands take a long time to install, and we
don't have any use for them on Travis, so we can speed up the build by
excluding them from "bundle install" entirely.
Restore --deployment to bundle install arguments

Travis adds this option automatically when it sees a Gemfile.lock, but
it's stopped doing it now that we're providing custom bundle install
arguments, so we should add it back to get the best of both worlds.
Add Travis build status image to README