Use a real build system

[sajacy]

This started as a hastily written script, then became a fun experiment with how to publish an extension.

There have been recent improvements (contributed by you fine Internet folks!), and some recent bugs that I've introduced - I had to publish 7 minor versions to get rid of silly errors (and still have some: #8). And this is the problem: there's no workflow to do testing and deployment.

Another opportunity is to improve the user experience. The Google Goal Seek extension is an example of a more refined UI, with controls in the sidebar. Imagine having a visual way to setup and manage data tables!

The extension runs with ES6 support in V8 now, so the script can also be refactored.

While this is still a fun passion project, it's time to get a bit more serious, and use yarn or gulp to build the main script, enable testing, a better UI (e.g. React sidebar), and easier deployment.

Open to discussion!