Updated SceneViewController to newer cluster paradigms

• `isClusterBaseClass` and `isClusterSubClass` changed to class methods
• `raiseNotImplementedInClusterClassExceptionForMethod:` changed to a class method and given a convenience patch-through instance method.
• `raiseNotImplementedInClusterClassExceptionForMethod:`'s NSException type changed to NSInternalInconsistencyException and message improved a bit.
• kClusterBaseClass static, initialized in `+ (void)initialize` and used in `raiseNotImplementedInClusterClassException()`.
• Now releases self in init's error case.
• Updated a couple of occurrences of `classfor(SceneViewController)` to `kClusterBaseClass` in SceneViewController.
• Error message in raiseNotImplementedInClusterClassExceptionForMethod: now uses the kClusterBaseClass constant to refer to the class name.