[BUGFIX] Fix BE tree

Because of removing IconUtility::getIconImage(), the code needs
to be changed to use the sprite API

Change-Id: I6ad386b869332085175eabe3fb5d1f40a54728ee
Reviewed-on: http://review.typo3.org/35135
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>