Add Rick W. Chen to Authors list.

Rick W. Chen has been nominated for author status twice, once in November 2010 and once again in January 2011. He has been with us since 2009, and he is undoubtedly one of the most prolific Amarok contributors of all time [1].
During the last discussion there seem to have been no objections over his author status, but he was never added to the About dialog, which is an unfortunate oversight.
The present commit corrects that oversight, and I'm happy to be the first to congratulate Rick on this recognition of his accomplishments.
[1] https://www.ohloh.net/p/amarok/contributors/14025215889458
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