[BUGFIX] Streamline calls to sysLog

Make all calls to GeneralUtility::sysLog use extkey "core"
instead of "Core".
Use constants for severity levels.
Fix wrong parameters (message instead of extension key).

Resolves: #68088
Releases: master
Change-Id: Iea44cff529b9d609f0815311e86e9549c20f83df
Reviewed-on: http://review.typo3.org/41170


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>