Author: Yuliya Bozhko
MDL-40924 badges: Add caching to external badges
http://git.moodle.org/gw?p=moodle.git;a=commit;h=129e7dffebdd229bc24f3c6d94db0ed1bab49c8d
http://github.com/moodle/moodle/commit/129e7dffebdd229bc24f3c6d94db0ed1bab49c8d
+ 2.5 en [badgesalt_desc,core_badges]
+ 2.5 en [error:externalbadgedoesntexist,core_badges]
+ 2.5 en [cachedef_externalbadges,core_cache]