Implement the custom role concept

- Custom Ansible roles can be stored in the `roles/custom` directory
- The list `custom_roles` determines which roles are included

roles/custom/fvs/files/fvs.menu

@@ -0,0 +1,12 @@
+<!DOCTYPE Menu PUBLIC "-//freedesktop//DTD Menu 1.0//EN"
+"http://www.freedesktop.org/standards/menu-spec/menu-1.0.dtd">
+<Menu>
+  <Name>Applications</Name>
+  <Menu>
+    <Name>FvS</Name>
+    <Directory>fvs.directory</Directory>
+    <Include>
+      <Category>fvs</Category>
+    </Include>
+  </Menu>
+</Menu>