Make it possible to add to selection menu in parental mode

[danners]

Hi, i like to run my kobo in parental mode for cleaned up interfaces etc. This PR makes selection menu additions also work in parental mode by searching for the last item in the selection menu in parental mode.

Thanks a lot for the great project !

[pgaskin]

Thanks! I'm somewhat buried in work and other commitments right now, but I'll review this as soon as I can.