Updated 'Game' class.

Updated the 'Game' class by adding the 'isColorTaken' method to it.

Projekte/mdga/model/src/main/java/pp/mdga/game/Game.java

@@ -96,6 +96,23 @@ public void updatePlayerActiveState(int id, boolean active) {
         this.players.get(id).setActive(active);
     }
 
+    /**
+     * This method will be used to check if the given color parameter is already taken.
+     * If yes it will return true, otherwise false.
+     *
+     * @param color as the color which should be checked if taken as a Color enumeration.
+     * @return      true or false.
+     */
+    public boolean isColorTaken(Color color) {
+        for (Map.Entry<Integer, Player> entry : this.players.entrySet()) {
+            if (entry.getValue().getColor() == color) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     /**
      * This method will be used to return the player which has the given id parameter.
      *