Make DefaultOrderByComparator a top-level class
LPS-34924 Push as much implementation to the descendant class as possible
LPS-34924 Finish refactoring base classes
LPS-34924 Apply to Article*Comparator
LPS-34924 Apply to AssetTag, BackgroundTask, DLContent
LPS-34924 Apply to Entry*Comparator
LPS-34924 Apply to Group*Comparator
LPS-34924 Apply to Item*Comparator
LPS-34924 Apply to Layout*Comparator