[FEATURE] Improve Thumbnail ViewHelper

It is now possible to retrieve a file in the Thumbnail VH
given a file identifier and a storage.
The change-set also adds a little tutorial in the README
how to display a list of files given various criteria.

Change-Id: I2ab7e07fba484dc65725839cc11785098c5b2d7b
Releases: 3.0.0
Resolves: #60954
Reviewed-on: http://review.typo3.org/32131
Reviewed-by: Fabien Udriot <fabien.udriot@ecodev.ch>
Tested-by: Fabien Udriot <fabien.udriot@ecodev.ch>