make class models, factories, controllers final

Author: mwunderl

src/main/java/scorekeep/GameModel.java

@@ -18,7 +18,7 @@ public class GameModel {
         .withRegion(Regions.fromName(System.getenv("AWS_REGION")))
         .build();
   private DynamoDBMapper mapper = new DynamoDBMapper(client);
-  private SessionModel sessionModel = new SessionModel();
+  private final SessionModel sessionModel = new SessionModel();
 
   public void saveGame(Game game) throws SessionNotFoundException {
     // check session