finalized dirt

added base for liquids

Scripts/Elements/Dirt.cs

@@ -11,10 +11,14 @@ public class Dirt : Solid {
     public override bool Update(int currentFrame) {
         if (!base.Update(currentFrame)) return false;
 
-        if (CheckBelow(X, Y)) {
-            _level.Swap(this, X, Y+1);
+        Vector2I freePos = Check(this, Vector2I.Down + Vector2I.Right);
+
+        if (freePos != Vector2I.Zero) { // diagonally right
+            _level.Swap(this, freePos);
+            return true;
         }
-        return true;
+
+        return true; // not necessarily end, subclasses could do some more things
     }
 
 }