refactor: add GUI instance reference to UI nodes

src/graphics/ui/elements/Panel.hpp

@@ -1,15 +1,16 @@
 #pragma once
 
-#include "commons.hpp"
 #include "BasePanel.hpp"
+#include "commons.hpp"
 
 namespace gui {
     class Panel : public BasePanel {
     public:
         Panel(
-            glm::vec2 size, 
-            glm::vec4 padding=glm::vec4(0.0f), 
-            float interval=2.0f
+            GUI& gui,
+            glm::vec2 size,
+            glm::vec4 padding = glm::vec4(2.0f),
+            float interval = 2.0f
         );
         virtual ~Panel();