Switch JS test to using intern

[Tom Aratyn]

This ticket is to translate the tests from from buster.js to theintern.

Buster.js is just not stable enough yet and my test framework can't be more brittle than my tests.

JavaScript tests should use http://theintern.io/.

This won't be super challenging as a task but might take some time to type. Both offer similar "object style" tests and their assert frameworks aren't very different.

Sinon.js should still be used where applicable.