WIP: zope4py3

Hi,

I tried to set up a erp5/py3 instance on Theia from slapos/zope4py3/software/erp5/software-py3 (as far as I understood https://www.erp5.com/group_section/forum/RFC--moving-to-python3-hiqp60J4cE this should be the state-of-the-art erp5/py3 development, isn't it?)

My zope process exited until I adjusted the SR with given changes.

I also adjusted the comment, because we currently use python 3.8 (see 1 and 2) (perhaps I should move the comment change in a separate commit).

Best, Levin

/cc @kazuhiko