Author: Jun Pataleta
MDL-66143 admin: Create setting for courses to support relative dates
http://git.moodle.org/gw?p=moodle.git;a=commit;h=afc87005cb8e0203dfb84d8fc246ede1c0e7145b
http://github.com/moodle/moodle/commit/afc87005cb8e0203dfb84d8fc246ede1c0e7145b
+ 3.8 en [enablecourserelativedates,core_admin]
+ 3.8 en [enablecourserelativedates_desc,core_admin]