Set script attribute of custom level script boxes

To avoid going through gamestates, we'll need to carry the name of the
script on the script box itself. And to do that, we'll need to set the
'script' attribute of script boxes when translating edentities into real
entities in custom levels.

desktop_version/src/Entity.h

@@ -53,7 +53,7 @@ public:
 
     void generateswnwave(int t);
 
-    void createblock(int t, int xp, int yp, int w, int h, int trig = 0);
+    void createblock(int t, int xp, int yp, int w, int h, int trig = 0, const std::string& script = "");
 
     bool removeentity(int t);