config: add mousepad configuration (dconf settings)

add a hook to update the systemd dconf database during build
https://help.gnome.org/admin/system-admin-guide/stable/dconf-custom-defaults.html.en
https://help.gnome.org/admin/system-admin-guide/stable/dconf-keyfiles.html.en
https://help.gnome.org/admin/system-admin-guide/stable/dconf-lockdown.html.en
https://help.gnome.org/admin/system-admin-guide/stable/dconf-profiles.html.en
Fixes #40

config/hooks/normal/0470-update-dconf-db.hook.chroot

@@ -0,0 +1,2 @@
+#!/bin/bash
+dconf update