Refactor to React

[Zarel]

I've been planning on a major refactor to React for a while now. This issue will keep track of what needs to be done, and construct something vaguely resembling a plan.

I've considered different approaches at rewriting one part at a time, but they all require basically the entire core to be rewritten, and maintaining two cores while writing everything else, which would be incredibly ugly. We're probably just going to need to maintain two clients and just copy-paste code from the old one to the new one.

[ghost]

@Zarel Any status update? I wanted to write a new Chrome/Firefox extension for the client. Just wondering if there was any time frame so I can decide on waiting or not.

[Zarel]

Um, no idea. I've done some preliminary work, but not enough to know exactly how long it'll take.

[Zarel]

This is now tracked in: #1156