Upgrade to new core APIs and libraries

:rotating_light: Work in progress :rotating_light:

This should not be merged until 0.142.0 is released.

* [x] Use addModalPanel API instead of direct DOM manipulation
* [x] Use atom-space-pen-views and space-pen libraries instead of deprecated exports
* [ ] Upgrade to a version of atom-space-pen-views that doesn't require `::detach` to be overridden