functional tests using phantomjs locally and saucelabs on travis-ci

Local tests pass. SauceLabs tests don't all pass, for various reasons.

IE is broken; a couple reasons we know of:
* https://github.com/mozilla/fxa-js-client-old/issues/35
* https://github.com/mozilla/fxa-js-client-old/issues/37 and `bind` uses in this repo

Tests also sometimes fail due to clock skew: https://github.com/mozilla/fxa-js-client-old/issues/36


Check these out @nchapman @shane-tomlinson. Shall we go ahead and merge so that we can continue with refactoring the Gruntfile?