[FEATURE] Make thumbnail size in file list configurable

The size of thumbnails of the file list is hard coded to
64x64 px which might not be optimal in some cases. Thus,
the size should be configurable via UserTS.

Releases: master
Resolves: #73357
Change-Id: Ibd3bd43e55231212a410ee56b375e9be5d4354d2
Reviewed-on: https://review.typo3.org/51306


Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Riccardo De Contardi <erredeco@gmail.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Markus Sommer <markus.sommer@typo3.org>
Tested-by: Markus Sommer <markus.sommer@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>