Make react the default editor

This will make react the default editor.

## Todo 
**this is not currently an exhaustive list, but we can use this to track the progress of the react editor**

* [ ] Fix gutter decorations https://github.com/atom/atom/issues/1984
* [ ] Don't show background tips behind editor https://github.com/atom/atom/issues/2383
* [ ] Make autocomplete-plus work with the react editor https://github.com/atom/atom/issues/2318