flex grid: add shortcut for Window

radio/src/thirdparty/libopenui/src/flexlayout.h

@@ -41,6 +41,8 @@ class FlexGridLayout
   {
   }
 
+  void apply(Window* w) { apply(w->getLvObj()); }
+
   void apply(lv_obj_t* obj) {
 
     // padding
@@ -56,6 +58,8 @@ class FlexGridLayout
     }
   }
 
+  void add(Window* w) { add(w->getLvObj()); }
+
   void add(lv_obj_t* obj) {
     if (col_dsc && row_dsc) {
         lv_obj_set_grid_cell(obj, LV_GRID_ALIGN_START, col_pos, col_span,