UColorCorrectRegionsSubsystem

World Subsystem responsible for managing AColorCorrectRegion classes in level. This subsystem handles: Level Loaded, Undo/Redo, Added to level, Removed from level events. Unfortunately AActor class itself is not aware of when it is added/removed, Undo/Redo etc in the level.

This is the only way (that we found) that was handling all region aggregation cases in more or less efficient way. Covered cases: Region added to a level, deleted from level, level loaded, undo, redo, level closed, editor closed: World subsystem keeps track of all Regions in a level via three events OnLevelActorAdded, OnLevelActorDeleted, OnLevelActorListChanged. Actor classes are unaware of when they are added/deleted/undo/redo etc in the level, therefore this is the best place to manage this. Alternative strategies (All tested): World's AddOnActorSpawnedHandler. Flawed. Invoked in some cases we don't need, but does not get called during UNDO/REDO AActor's PostSpawnInitialize, PostActorCreated and OnConstruction are also flawed. AActor does not have an internal event for when its deleted (EndPlay is the closest we have).