add move frame buttons

src/node_panel_animation.h

@@ -52,6 +52,8 @@ class NodePanelAnimation : public Node
     NodeButtonCustom* btn_remove = nullptr;
     NodeButtonCustom* btn_up = nullptr;
     NodeButtonCustom* btn_down = nullptr;
+    NodeButtonCustom* btn_left = nullptr;
+    NodeButtonCustom* btn_right = nullptr;
     NodeButtonCustom* btn_duplicate = nullptr;
     Node* m_layers_container = nullptr;
     Node* m_frames_container = nullptr;