refactor map handling and improve tile initialization logic

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

@@ -1,13 +1,23 @@
 package de.miaurizius.jgame2d.core;
 
 import javax.swing.*;
+import java.io.FileNotFoundException;
+import java.io.IOException;
 import java.util.logging.Logger;
 
 public class Boot {
 
     public static final Logger logger = Logger.getLogger("JDGame2D");
     public static JFrame window;
-    public static GamePanel gamePanel = new GamePanel();
+    public static GamePanel gamePanel;
+
+    static {
+        try {
+            gamePanel = new GamePanel();
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
 
     static void main() {
         generateWindow();