Fix for [#34934] Freestyle options are in wrong tab.

Added a label to guide users to line style settings in the Render Layers context
(in line with the similar labels found in the Cloth and Soft Body modifier panels),
so that Freestyle options per render layer can be more easily found.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55929 954f8c5b-7b00-dc11-b283-0030488c597c