[FEATURE] Add Thumbnail Generator tool for generating thumbnails

Change-Id: I1297a7437bfc96b48d6f85bc634e1816c15d826c
Releases: 3.1
Resolves: #61652
Reviewed-on: http://review.typo3.org/32809
Reviewed-by: Fabien Udriot <fabien.udriot@ecodev.ch>
Tested-by: Fabien Udriot <fabien.udriot@ecodev.ch>