Creates a new JFC (Swing) internal frame that can be placed
onto a JDesktopPane to provide an MDI user interface. Typically you would create
an internal frame class containing display elements
for each individual frame.  Treat each internal frame class like a JFrame
class. Then create a JFrame (or JApplet) application with a JDesktopPane on it.  Add the
internal frames to the desktop pane using code, or using the Copy and Paste functions
in the Projects window after the internal frames are compiled.