Adds sub-object specific clean functions to prevent breaking with lv_obj_clean

lv_objx/lv_page.h

@@ -79,6 +79,12 @@ typedef enum {
  */
 lv_obj_t * lv_page_create(lv_obj_t * par, lv_obj_t * copy);
 
+/**
+ * Delete all children of the scrl object, without deleting scrl child.
+ * @param obj pointer to an object
+ */
+void lv_page_clean(lv_obj_t *obj);
+
 /**
  * Get the scrollable object of a page
  * @param page pointer to a page object