add preset popup menu

src/layout.h

@@ -34,10 +34,16 @@ public:
         auto i = m_layouts.find(id);
         return i == m_layouts.end() ? nullptr : i->second.get();
     }
-    class std::shared_ptr<Node> get_ref(const char* name)
+    template<class T = Node> std::shared_ptr<T> get_ref(const char* name)
     {
         auto i = m_layouts.find(const_hash(name));
-        return i == m_layouts.end() ? nullptr : i->second;
+        return i == m_layouts.end() ? nullptr : std::dynamic_pointer_cast<T>(i->second);
+    }
+    template<class T = Node> std::shared_ptr<T> instantiate(const char* name)
+    {
+        if (auto layout = get_ref(name))
+            return layout->m_children[0]->clone<T>();
+        return nullptr;
     }
     void restore_context();
     void clear_context();