Summary:
Better error handling in the account settings page and a loading spinner
Add Account... replaces "Link External Account", and it works
Clean dead code from onboarding pages, remove base class component
Always show the account switcher
rm dead EdgehillAPI code, AccountStore now manages accounts and credentials in config, not in database
Fix specs
Test Plan: Run tests
Reviewers: dillon, evan
Reviewed By: evan
Projects: #edgehill
Differential Revision: https://phab.nylas.com/D2059