[BUGFIX] Filelist: make CSH useable

In the "new" view of filelist the CSH is not useable because it is
located inside the label tag. This patch adjusts the markup.

Additionally a CSH for adding media assets is added.

Change-Id: I9deab9f747c54c2a4e8f3b4ee987d71cd6027f1f
Resolves: #72512
Releases: master, 7.6
Reviewed-on: https://review.typo3.org/45558


Tested-by: Gianluigi Martino <gmartino27@gmail.com>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>