Gracefully remind WordPress users about Waltz

- [x] After 3 successful logins, show numbered badge in Clef settings menu title
- [x] After 3 successful logins, show dismissible Waltz notification on Clef settings page
- [x] After 15 successful logins, if Clef settings Waltz notification hasn't been dismissed, show a one-time notification on the admin dashboard
- [x] None of the above things should happen if Waltz is already installed