CHANGELOG.md: Add "Fixed" line for issue #654

Author: torss

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 ## [NEXT] 
+### Fixed
+- Fixed wasteful course data usage #654 via specialized course model interfaces.
 
 
 ## [0.6.0] - 2018-03-31 - Introduces MediaManager and some minor changes