Draft: small py2 fixes, port to py3 and enable & apply fixes for GitlabCI

WIP py3 porting, left as draft for visibility. Deferred to until the server is migrated to 22.04. 18.04's py3.5 has poor out-of-the-box locales configuration and iirc does not work with attobuild's python.

Can someone with org access to TMWA add an attobuild repo copied from https://git.themanaworld.org/specing/attobuild so that the submodule link can be updated to no longer refer to my personal repo?

I have squashed what was sensible from my perspective. If you would prefer the full, 32 commit version, say so, and I may bring it out of reflog.