Comment 10 for bug 1659256

I implemented what I described in #9 now, see
https://gitlab.com/inkscape/inkscape/merge_requests/180

I also fixed the "small" window size options but chose to set it to an initial 600x600 now, as I think everything smaller is not really usable anyway (at least with common gtk3 themes) - we can obviously discuss this further if somebody thinks an even smaller window would be useful.