Add RadioButton, fixes #265
Squash from  sbrunot/deliteful:intern-2.0.1
Trying to use BrowserStack.

1. Add new intern.browerstack.js file, which may eventually replace intern.js
   (which connects to SauceLabs).   For now, run it via:

$ grunt test:browserstack

after setting up BrowserStack account, and BROWSERSTACK_USERNAME and BROWSERSTACK_ACCESS_KEY
environment variables.

2. upgrade to intern 2.0.3 (and thus leadfoot 2.0.2)

3. add node_modules to excludeInstrumentation list
Fix Slider functional tests timeout issues.
Rebase migration branch on master. Migrate new tests to Intern 2.0.1.
Fix issues reported by jshint.
All tests are now using the same timeout and poll interval values,
defined only once in the intern configuration file.
Fix functional tests.
Fix test pages to use deliteful's boilerpate.js.
Run automated tests on Firefox 31 instead of Firefox 25.
intern-2.0.1 branch rebased on master to take into account updates of
the CheckBox tests.
Fix CheckBox functional tests.