Add GameState#needs_repaint? and Container#remove

lib/cyberarm_engine/game_state.rb

@@ -34,6 +34,10 @@ module CyberarmEngine
       true
     end
 
+    def needs_repaint?
+      true
+    end
+
     def drop(filename)
     end
 

lib/cyberarm_engine/ui/elements/container.rb

@@ -42,6 +42,10 @@ module CyberarmEngine
         root.gui_state.request_recalculate
       end
 
+      def remove(element)
+        root.gui_state.request_recalculate if @children.delete(element)
+      end
+
       def clear(&block)
         @children.clear