[Bug-gnubg] About box

[Jon Kinsey]

I've reorganized the about box a bit, mainly moving some of the text off 
to different screens.  One with info about the build and another with 
the credits.

I've added some specific credits (I guessed some...) for the translators 
and the help/support work.  I've also (in one of my less selfless 
moments) added myself to the credits.

I like the idea of more specific credits, what does everyone think?

Jon