NSPastboard additions to support reading and writing view controllers.
Superclass: NSPasteboard
NSPastboard additions to support reading and writing view controllers. MOViewControllers are written to the pasteboard using their state dictionaries as the persistent representation (by calling -stateDictionaryIgnoringContentState:). They are read back by recreating the controller hierarchies using the +viewControllerWithStateDictionary:ignoringContentState: factory method. This means that if you pass a controller through the pasteboard, you get a new equivalent controller hierarchy when you take it back out, you do NOT get the original controller hierarchy. Note that this also means that the new hierarchy will be equivalent only to the extent supported by its state dictionary. If a controller subclass fails to save and restore some aspect of its state, that aspect will be lost when the controller passes through the pasteboard.