Write tests for the Chrome UserWeb Extension

[MarkIannucci]

Describe the bug
The code doesn't have tests. We need to identify a framework for unit tests and refactor the code so it can be tested automatically. This probably means moving the bulk of the work done by the event into a function which returns the newURL and then a test which confirms that the url for the entered string is what we want.

[christopherpickering]

Hey if you are open to javascript tests and coverage, I'm willing to add tests for the background.js script using ava.