- DrawablesManager class now inherits from ContainerObserver instead of inheriting from Observer.
- Visibility of the ContainerObserver::notifyElementAction() method has been changed from private to protected.
- The order of the arguments for the ContainerObserver::notifyElementAction() has been changed.
- Added missing calls to addObserver() in DrawablesManager constructor.
- Added a destructor for DrawablesManager which calls to removeObserver() on all the DrawablesSelection instances held by the class.