Switch from zombie.js to selenium

Tear out all the zombie.js test code and replace it with selenium, with
the hope that this will result in greater stability and test
deterministicness, and the option to move to node v0.10.
Fix getText on phone-hidden elements

Selenium returns empty string for getText on hidden elements.
Headlessly running selenium can result in the username being hidden from
the toolbar. So execute a script to grab it directly rather than relying
on getText.