[TASK] Change flashmessages.js for new FlashMessage styling

Resolves: #62605
Releases: master
Change-Id: I896bb14d39ac5f0fd32c511084b23fc3e2ba71af
Reviewed-on: http://review.typo3.org/33695
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>