Add category to desktop file and minor clean up.

This relates to issue #24.

Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>
Signed-off-by: Darrell Anderson <darrella@clovermail.net>
(cherry picked from commit 9ca0bb40a2)

knights/knights.desktop

@@ -7,7 +7,7 @@ Name=Knights
 GenericName=Chess Game
 Comment=A graphical chess interface
 X-TDE-InitialPreference=1
-MimeType=application/x-chess-pgn,Application
-X-TDE-ServiceTypes=
+MimeType=application/x-chess-pgn
 X-DocPath=knights/index.html
 Terminal=false
+Categories=Qt;TDE;Game;BoardGame;