Change <pre> tags in qunit code to <code> instead to work around an env.js bug

http://envjs.lighthouseapp.com/projects/21590-envjs/tickets/176
Add mocha and coffee-script as development dependencies in the Gemfile
Refactor rhino runner js to return the correct json
Refactor QUnitTestResult.symbolize_keys to change keys in nested hashes & arrays
Remove unit test for an empty js test file
Comment out logging of userAgent by envjs, to make rhino driver test pass