[gtk-osx] Improve top menu integration for App part

Move some menu items to the MAC specific menu named 'dia'.
At least About and Preferences belong their, also hide the
File/Quit entry to avoid redundance.
For further application wide entries like 'Diagram Tree' and
'Sheets and Objects' the movement is prepared, but not done yet.
[gtk-osx] Update installer/macos for non-X build

 - remove now unsupported --integrated command line switch
 - update the icon to be closer to the other platforms
   application icons
 - change osx-app.sh for backend releated file changes