Define an app-menu with About & Quit actions

Rename some paths for auto resource magic

hammond-gtk/resources/gtk/headerbar.ui

@@ -364,6 +364,7 @@ Tobias Bernard
             <property name="can_focus">True</property>
             <property name="receives_default">False</property>
             <property name="text" translatable="yes">About</property>
+            <property name="action-name">app.about</property>
           </object>
           <packing>
             <property name="expand">False</property>

hammond-gtk/resources/gtk/menus.ui

@@ -0,0 +1,30 @@
+<?xml version="1.0"?>
+<interface>
+  <!-- interface-requires gtk+ 3.0 -->
+  <menu id="app-menu">
+    <section>
+      <item>
+        <attribute name="label" translatable="yes">_Preferences</attribute>
+        <attribute name="action">app.preferences</attribute>
+      </item>
+    </section>
+    <section>
+      <item>
+        <attribute name="label" translatable="yes">_Keyboard Shortcuts</attribute>
+        <attribute name="action">win.show-help-overlay</attribute>
+      </item>
+      <item>
+        <attribute name="label" translatable="yes">_Help</attribute>
+        <attribute name="action">app.help</attribute>
+      </item>
+      <item>
+        <attribute name="label" translatable="yes">_About</attribute>
+        <attribute name="action">app.about</attribute>
+      </item>
+      <item>
+        <attribute name="label" translatable="yes">_Quit</attribute>
+        <attribute name="action">app.quit</attribute>
+      </item>
+    </section>
+  </menu>
+</interface>