Migration of acceptance test from Selenium RC to Webdriver, Saucelabs integration

Once we add the proper [secure environment variables](http://about.travis-ci.org/docs/user/build-configuration/#Secure-environment-variables) to our `.travis.yml` (which this pull request doesn't do), we'll be able to run the acceptance test(s) as part of our Travis CI, which will be awesome.

Right now I've killed off the failing issuer frame test because the code that supported it is gone, so we've only got one acceptance test now, which simply logs into the backpack. But this is the start of a brave new acceptance-testing world!