[BUGFIX] config.pageTitleSeparator not known by t3editor

Change-Id: Ia055fb8aceb50271bf25e5d15b56d9dcde13a5aa
Fixes: #39600
Releases: 6.0, 4.7
Reviewed-on: http://review.typo3.org/13613
Reviewed-by: Tobias Liebig
Tested-by: Tobias Liebig
Reviewed-by: Wouter Wolters
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer