[BUGFIX] CE:Image - backend preview of image order

The Backend preview does not reflect the sorting of the elements in the
content element. This patch added the sorting field from the TCA to the
thumbCode method.

Resolves: #48645
Releases: 6.2, 6.1, 6.0
Change-Id: I9dcec1c2baae226aeded9c4c93d368c067c0bad2
Reviewed-on: https://review.typo3.org/22028
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn