Summary:
Fix label sorting... apparently we just synced them in creation date order
Allow labels / folders to be nested using separators `.`, `/`, and `\`
Allow collapsing of nested labels in sidebar
Add overflow hidden to some core flexboxes, which dramatically reduces repaints because it knows columns will not overflow into other columns
Prevent scroll region contents from re-rendering all the time, not sure why this works
Add test for account sidebar store
Test Plan: Run new test of AccountSidebarStore
Reviewers: evan
Reviewed By: evan
Differential Revision: https://phab.nylas.com/D2181
a83201ef7e