Author: Dmitrii Metelkin
MDL-66667 course: add course image cache
http://git.moodle.org/gw?p=moodle.git;a=commit;h=88a150467fd304ba5d05dfe661e74336a70956c1
http://github.com/moodle/moodle/commit/88a150467fd304ba5d05dfe661e74336a70956c1
+ 3.11 en [cachedef_course_image,core_cache]