Rewrite using TypeScript/React?

[mcmire]

The JavaScript is getting quite unwieldy (it's already at 1200+ lines). It would be nice to rewrite this project in a way that would be more representative of a real-world project. We use React in the extension already, so that seems like a natural progression. We might also consider using Redux (but that is optional). Also, we want to transition to TypeScript and we might as well switch this project to that.