gio: Add newer dbus UnknownXxxx and PropertyReadOnly errors

Add G_DBUS_ERROR codes for:

 * org.freedesktop.DBus.Error.UnknownObject
 * org.freedesktop.DBus.Error.UnknownInterface
 * org.freedesktop.DBus.Error.UnknownProperty
 * org.freedesktop.DBus.Error.PropertyReadOnly

These were discussed on the dbus mailing list
and introduced in the following libdbus commit:

2c34514620c4b79ea4ec71d1db583379138d01ac

https://bugzilla.gnome.org/show_bug.cgi?id=727900