A new event ``modal-destroyed`` is triggered after modals dismissed.

Change-Id: Id05bf17889889bf1bacbd6a6ad3023923899671d
Resolves: #73720
Releases: master
Reviewed-on: https://review.typo3.org/46933


Reviewed-by: Jan Helke <typo3@helke.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>