[RELEASE] Release of TYPO3 4.6.18

Change-Id: I858b4d638f1bc415a29b6b0d3a276020ee85b9e0
Reviewed-on: https://review.typo3.org/18773
Reviewed-by: TYPO3 Release Team
Tested-by: TYPO3 Release Team
[TASK] Set TYPO3 version to 4.6.19-dev

Change-Id: Ic57d3af1091872b96d3b04a6959a5969a0c4aa08
Reviewed-on: https://review.typo3.org/18774
Reviewed-by: TYPO3 Release Team
Tested-by: TYPO3 Release Team