rework on graphics.cpp, implement some GFX with lua

modules/mainmenu/ui/entergamewindow.otui

@@ -50,4 +50,4 @@ MainWindow
     anchors.bottom: parent.bottom
     margin.bottom: 16
     margin.right: 16
-    onClick: function(self) self.parent:destroy() end
+    onClick: function(self) GFX.fadeOut(self.parent) end

modules/mainmenu/ui/mainmenu.otui

@@ -10,7 +10,7 @@ Panel
     smooth: true
   anchors.fill: parent
 
-  RoundedGridPanel
+  RoundedPanel
     id: mainMenu
     size: 144 162
     anchors.left: parent.left
@@ -23,7 +23,10 @@ Panel
       anchors.top: parent.top
       anchors.horizontalCenter: parent.horizontalCenter
       margin.top: 18
-      onClick: rootWidget:addChild(loadUI("/mainmenu/ui/entergamewindow.otui"))
+      onClick: |
+        local enterGameWindow = loadUI("/mainmenu/ui/entergamewindow.otui")
+        rootWidget:addChild(enterGameWindow)
+        GFX.fadeIn(enterGameWindow)
 
     MenuButton
       text: Options