[TASK] Use a larger preview image in show_item (launchView)

Increase the size of the image in show_item (launchView).
This window is displayed when a image in list or file_list is clicked.

Change-Id: I5b347a15c04b082b015d99fb2e80d486667a3398
Resolves: #28963
Releases: 4.6
Reviewed-on: http://review.typo3.org/4307
Reviewed-by: Susanne Moog
Tested-by: Susanne Moog
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn