Summary:
Focused Content Store should notify observers when focused items change, not just when they're reassigned
Popovers should have a `direction` and optional event onOpened
Menu divider documentation was wrong, menus should support checked items by default
Pressing escape in a popover's input should dismiss the popover
Other changes
Remove specs that make no sense anymore
Small tweak to report build breaking. Shouldn't happen often ;)
Test Plan: Run tests, which will now phone home if they break
Reviewers: evan
Reviewed By: evan
Differential Revision: https://review.inboxapp.com/D1493
