example: Use a menu model for primary menu

Signed-off-by: Alexander Mikhaylenko <alexm@gnome.org>

examples/hdy-demo-window.ui

@@ -3,25 +3,14 @@
 <interface>
   <requires lib="gtk+" version="3.16"/>
   <requires lib="libhandy" version="1.0"/>
-  <object class="GtkPopover" id="menu_popover">
-    <child>
-      <object class="GtkBox">
-        <property name="visible">True</property>
-        <property name="spacing">6</property>
-        <property name="margin">18</property>
-        <property name="orientation">vertical</property>
-        <property name="width_request">200</property>
-        <child>
-          <object class="GtkModelButton">
-            <property name="action-name">app.preferences</property>
-            <property name="can-focus">True</property>
-            <property name="text" translatable="yes">Preferences</property>
-            <property name="visible">True</property>
-          </object>
-        </child>
-      </object>
-    </child>
-  </object>
+  <menu id="primary_menu">
+    <section>
+      <item>
+        <attribute name="label" translatable="yes">Preferences</attribute>
+        <attribute name="action">app.preferences</attribute>
+      </item>
+    </section>
+  </menu>
   <template class="HdyDemoWindow" parent="GtkApplicationWindow">
     <property name="can_focus">False</property>
     <property name="title">Handy Demo</property>
@@ -48,7 +37,8 @@
                     <property name="visible">True</property>
                     <property name="can_focus">True</property>
                     <property name="focus_on_click">False</property>
-                    <property name="popover">menu_popover</property>
+                    <property name="menu_model">primary_menu</property>
+                    <property name="use_popover">True</property>
                     <child>
                       <object class="GtkImage">
                         <property name="visible">True</property>