[BUGFIX] ConfigurationManager must use namespaced FrontendSimulator

Since TYPO3 6.0 all classes are namespaced.
Though a compatibility layer exists all calls on old
class names should be avoided, so this patch replaces
calls on Tx_Extbase_Utility_FrontendSimulator with
\TYPO3\CMS\Extbase\Utility\FrontendSimulatorUtility.

Releases: 6.1, 6.0
Fixes: #44806
Change-Id: I60dd5f4fee8d5df8a79bb931e946a867b0083291
Reviewed-on: https://review.typo3.org/17703
Reviewed-by: Wouter Wolters
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind