Summary: This diff makes plugin loading async, which we'd need in a browser env (either because we'd use `import()` or we need to fetch the source and than eval it), and deals with all the fallout of that
Reviewed By: timur-valiev
Differential Revision: D32669995
fbshipit-source-id: 73babf38a6757c451b8200c3b320409f127b8b5b