Author: Paul Holden
MDL-82399 admin: allow selective purging of courses cache from UI.
Equivalent to the same functionality in the CLI tool in 5e05ad570f.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=c78793beb3f76146d9a5634b9616ace3e9ead479
http://github.com/moodle/moodle/commit/c78793beb3f76146d9a5634b9616ace3e9ead479
+ 5.0 en [purgecoursecache,core_admin]