invite 5.x-1.6

New features:
- #86875: Deleting invites of users that are about to be deleted. Orphaned invites will be cleared out when visiting http://www.example.com/update.php.
- #118823 Invite API: Add inviter to API arguments when deleting an invitation.
- Reusing user_password() for invite code generation.

Bugs fixed:
- #118849: Fixed missing delete link, despite "Allow deletion of joined users" is enabled (only true for deleted user accounts).
- #110795: Fixed the possibility for a maliscious user to reuse one invitation code over and over again.
- #106962: Fixed misleading watchdog error 'Registration code failed'.
- #106962 by knseibert: Fixed changed form_id for user settings form (5.x only).
- #118826: Verifying the user that tries to delete an invite. Previously it was possible to delete arbitrary invites if you knew its email address (or by using brute-force methods).
- Fixed several missing checks for an expired invitation code when a user tries to register.
- Fixed doubled expiration time calculation on invites page.
- Fixed unblocking of new user accounts, which was not limited to invite only mode. This broke sites where administrator approval for new user accounts is required.
- Fixed the notification that is displayed for the inviter when an invited user registers.
- Fixed queries for PostgreSQL.
- Fire 'invite' API event only if send was successful.
- Updated the database scheme to be more performant.