WIP: Python3

This is a merge request to track ERP5 support for Python3 (zope4py3 branch). See also the following merge requests:

• Python3 business template support.
• IdTool: handle bytes for group_id on python3.
• !2131 (merged)
• !2136 (merged)

Using https://lab.nexedi.com/nexedi/slapos/merge_requests/1257 https://lab.nexedi.com/nexedi/slapos/-/merge_requests/1670 for slapos.