[TASK] Use t3lib_BEfunc instead of date()

use t3lib_BEfunc::date and ::datetime() instead
of native date().

Change-Id: Ie8679c345efabd5415f2f9bde1e6f9f4f31239ce
Resolves: #23055
Releases: 4.7
Reviewed-on: http://review.typo3.org/7780
Reviewed-by: Philipp Gampe
Reviewed-by: Wouter Wolters
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter
Reviewed-by: Dominik Mathern
Tested-by: Dominik Mathern