clean code: extract inner classes

src/main/java/eu/midnightdust/yaytris/Tetris.java

@@ -3,7 +3,8 @@ package eu.midnightdust.yaytris;
 import eu.midnightdust.yaytris.game.Space;
 import eu.midnightdust.yaytris.ui.ScoreMenu;
 import eu.midnightdust.yaytris.ui.TetrisUI;
-import eu.midnightdust.yaytris.util.SoundUtil;
+import eu.midnightdust.yaytris.util.GravityTimerTask;
+import eu.midnightdust.yaytris.util.sound.SoundUtil;
 
 import javax.swing.*;
 import java.time.LocalTime;
@@ -48,6 +49,15 @@ public class Tetris {
         return space;
     }
 
+    /**
+     * Get the ui instance
+     *
+     * @see          TetrisUI
+     */
+    public static TetrisUI getUi() {
+        return ui;
+    }
+
     /**
      * Resets the game space, preparing it for a new game.
      *
@@ -127,17 +137,4 @@ public class Tetris {
         }
     }
 
-    /**
-     * Defines our custom timer task that handles falling pieces.
-     */
-    public static class GravityTimerTask extends TimerTask {
-        @Override
-        public void run() {
-            if (space.getCurrentTetromino() != null) {
-                updateTime();
-                space.getCurrentTetromino().fall();
-                ui.getGamePanel().repaint();
-            }
-        }
-    }
 }