Mocha Tests for Scan.js

First round of testing. Right now this only include a test for the .innerHTML rule, but my last branch bit-rotted so I figured it'd be good to get it in incrementally.

I'll create another PR , after this is merged into master, which tests all the rules! :chicken: 

I removed a few commented out console.logs as well as a few console.logs that were causing errors in the web workers. @mozfreddyb is working on a PR that will address that, so those console.logs will probably be added back in then.