add findGameById-Method

fh.fd.ci.server/src/main/java/de/fd/fh/server/game/GameService.java

@@ -25,6 +25,11 @@ public class GameService
         return (GameId) repository.save(game).getId();
     }
 
+    public Game findGameById(final GameId gameId)
+    {
+        return repository.findByGameId(gameId);
+    }
+
     private Set<Field> initFields(UserId blackUser, UserId whiteUser)
     {
         final Set<Field> fields = new HashSet<>();