add MiniMap functionality and integrate map state handling

src/de/miaurizius/jgame2d/core/UI.java

@@ -17,10 +17,10 @@ public class UI {
 
     GamePanel panel;
     Graphics2D graphics2d;
-    Font font;
     BufferedImage heart_full, heart_half, heart_blank, coin;
     ArrayList<String> messages = new ArrayList<>();
     ArrayList<Integer> messageCounter = new ArrayList<>();
+    public Font font;
     public String currentDialogue;
     public Entity tradingNPC;
     public int commandNum;