Loading and Saving Whistles

• Load Whistle: Load a whistle from file, it becomes the current whistle;  the previously current whistle is still in memory - you can find it by name in the 'View' menu.
• Load Whistle (replace current) : Load a whistle from file, and it replaces the current whistle.  Any information about the previously current whistle is lost.
  
• Save Whistle: Save the current whistle.  The current whistle stays in memory, but its name changes to the saved filename.
• New Whistle: Create a new whistle in memory; The current whistle is still in memory - you can find it by name in the 'View' menu. The new whistle will not have a name.
• New Whistle (replace current): Create a new whistle in memory that replaces the current whistle. Any information about the previously current whistle is lost. The new whistle will not have a name.
• Unload Whistle: Remove the current whistle from memory.  If there another another whistle in memory it will become the current whistle.  If there is no other whistle in memory then a new one is created and made the current whistle.  The new whistle will not have a name.
• Exit: exit the program.