[CLEANUP] Cleanup ext:core/Configuration

* Use one use-statement per class
* Format phpDoc correctly

Resolves: #62705
Releases: master
Change-Id: If199c6962eeff31789742a05ddfd0b37d89b0079
Reviewed-on: http://review.typo3.org/33801
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>