Adds a PropertyChangeListener to the listener list.
In the future, this should prompt for save if the app is dirty.
Property currentFileOpened indicates if the current file has ever been opened. This is to handle the initial state where the current file is set, but should not be displayed because it has not been opened.
Getter for property dirty.
Property loading is true when a load operation is being performed.
Property saving is true when a save operation is being performed.
Removes a PropertyChangeListener from the listener list.
Setter for property currentFileOpened.
Setter for property dirty.