Serve React bundle and admin CSS bundle remotely

## The plan

Serve both our React JS bundle(s) remotely as well as the accompanying CSS. Serving these remotely could speed up the loading of the React bundle on sites, decrease load on hosts, allow for bug fixes without the need for a point release (also decreasing load on hosts), and allow for us to make/undo changes depending on feedback from the people using Jetpack.
## Requirements
- [ ] Needs to serve JS bundle from our CDN.
- [ ] Needs to serve admin CSS from our CDN.
- [ ] Need to be able to manage versions (and cache bust)
- [ ] Needs to be a way to opt out of using the remote bundles.
- [ ] Needs to have fallbacks for both that are bundle with JP. Fallbacks should be used in dev mode, if our CDN is down/blocked, or if a user opts out.
## Project management

We may use one of these new fangled Github projects to manage this. I'll leave that decision up to those assigned to work on this task.
## Designs

TBD. We need to design a way for people to opt out (or in). It's probably going to be a setting somewhere. _shudder_

.

```
updated Wed Oct 26 17:01:07 PDT 2016

♜ ♞ ♝ ♛ ♚ ♝ ♞ ♜
♟ ♟ ♟ ♟ ♟ ♟ ♟ ♟
… … … … … … … …
… … … … … … … …
… … … … ♙ … … …
… … … … … … … …
♙ ♙ ♙ ♙ … ♙ ♙ ♙
♖ ♘ ♗ ♕ ♔ ♗ ♘ ♖

♚'s turn.
```

The issue names no files, tests, or entry points. Start by resolving the TBD opt-out design and defining CDN versioning, cache busting, fallback, and development-mode behavior; done means both React JS and admin CSS bundles meet every listed requirement.

Written by the indexing model from the issue text.