[FEATURE] Introduce DataProcessor for media galleries

The logic for working with galleries and calculating the maximum media
size is done in a separate galleryProcessor.

Resolves: #67663
Releases: master
Change-Id: If00c3b800b2c6723d923cb3e3d427b850f9be7fe
Reviewed-on: http://review.typo3.org/40509


Reviewed-by: Frans Saris <franssaris@gmail.com>
Tested-by: Frans Saris <franssaris@gmail.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Patrick Broens <patrick@patrickbroens.nl>
Tested-by: Patrick Broens <patrick@patrickbroens.nl>