refs https://github.com/TryGhost/Product/issues/3504
- App component now uses React hooks intead of React class component
- App is now written in TypeScript
- All JavaScript is now removed from the Comments-UI project
- Removed `PopupNotification` because these were never displayed
- Removed `action` from AppContext (never used)
- Moved options parsing out of `index.ts` into a separate utility file,
similar to the signup-form
- Improved reliability of some editor tests by always waiting for the
editor to be focused (was not always the case) + added an utility method
for this
refs https://github.com/TryGhost/Team/issues/3504
This migrates comments-ui to TypeScript. Only `App.js` is left to
migrate, but since this isn't using hooks yet, it will need a bigger
rewrite so this will need to happen in a separate PR.
