[TASK] Set TYPO3 version to 6.3-dev

Releases: 6.3
Change-Id: Ie6aef74f866ac9b93e752a777ce6313126d8a32f
Reviewed-on: https://review.typo3.org/30786
Reviewed-by: Christian Kuhn
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader