Added background() method.
Added image() method.
Added setImageFile() method.
Updated setFilePath method to generate icons from images in memory when possible.
Fixed object editor widget not setting background image.
Added removeItem method.
Added objectAdded and objectRemoved signals.
Added new QDockWidget for listing Scene objects.
Added new ObjectsView class to list Scene objects.
Implemented ObjectsView in main window.
Fixed crash when changing states in character.