[TASK] Update NEWS.txt and INSTALL.txt

Change-Id: Id6be33c7b6073ce801aa0a9e3b7b75f6964ef2c3
Releases: 6.0
Reviewed-on: http://review.typo3.org/16782
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Dmitry Dulepov
Tested-by: Dmitry Dulepov
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader