Merge email and remote sharing

Merge email and remote sharing: To prevent showing an email-adress (or Federated Cloud ID) twice in the sharing with user dropdown, I'd propose to merge them into one single "[email protected]"-entry ... Clicking on it will first check whether there is an Federation server (remote, prioritized), and if not - It will use email as fallback method (because it makes no sense to share with somebody who as Nextcloud himself via email).