Moved all autocomplete view logic from PLEditorViewController into PLAutocompleteViewController.

PLAutocompleteViewController is now initialized with a NSTextView object. It then adds its view as a subview of the text view and registers as an observer for two NSTextStorage notifications and one NSText notification. The related logic from the PLEditorViewController delegate methods are moved into the appropriate notification method body. PLEditorViewController is no longer a NSLayoutManagerDelegate. It now simply allocates a PLAutocompleteViewController and provides its autocomplete data.
PLAutocompleteController now provides a factory method rather than a initWithTextView: method for initialization.

Initialization now occurs in the initWithNibName:bundle method with its textView instance variable set to nil. The factory method calls this method and initializes the textView with setTextView:. This method registers the autocomplete view for notifications with the text view and removes it from notifications with the previous text view.