Summary:
Fixes T3568
The composer windows had the wrong cache in their `ContactStore`s. Since
it's VERY expensive to repopulate a ContactStore's cache, we now have a
`WindowBridge` that allow you to, with a Promise, invoke methods on the
main window instead.
(Still need to fix some tests)
Test Plan: Fixed tests
Reviewers: dillon, bengotow
Reviewed By: dillon, bengotow
Maniphest Tasks: T3568
Differential Revision: https://phab.nylas.com/D2045
