Deprecate exports

### TODO

* [x] Deprecate space-pen exports
* [x] Deprecate React exports
* [x] Add event-kit exports
* [ ] Docs
  * Fix places where it's getting `View` and `$` from `atom`
  * Add a little blurb about the deps with the hats

Closes #3842
Yup, packages will reuse this one as long as the version they depend on is compatible with this one