Change image for "about" dialogue

[Bastián Díaz]

John, now that you've added support for scalable version of the application 
icon, could redirect the image to be used in the about dialogue in a larger 
size? (eg. 128x128).

I really do not know how to make that change and do not want to break something.

In the last update I changed the icon for about dialogue by the 
applicationicon, since many applications use the same configuration and it 
seemed the most appropriate. Now with support scalable icon, it is not 
necessary to duplicate the same image.

Thanks in advance.

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Bastián Díaz