[TASK] Improper category of extension

This extension is now much more in category "Backend modules" than
"TYPO3 services".

Change-Id: I334963b2e798decea7d1782d5c32b34c1e7e6331
Reviewed-on: https://review.typo3.org/27099
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers