add qudt namespace

[pvgenuchten]

the qudt namespace is quite used with sosa/ssn, suggestion to add it, also adds a warning if a term from a namespace is used which is not registered, instead of trying to parse as None.

• add qudt namespace
• warn for term in missing namespace

[ceteri]

@pvgenuchten, i've tried to merge all the PRs
this one has some merge conflicts to be resolved, though it looks minor

also, may i transfer ownership of csvwlib to you?

[pvgenuchten]

Hi, I’ll rework PR’s
Thanx for offering ownership, love to make a new pypi release, connect on Bluesky?