Thank you mypy, very cool. These types make things *so much better*.
They don't just complicate everything and don't really help because they
can not detect that an element queried by a tag is no navigable
string...
Also uses urljoin() in a few places that previously used string
concatenation or fstrings.
At this point, there isn't yet a need for IliasConfig, so I'd rather
keep the code base simpler and more consistent. Should we need a
structure like IliasConfig in the future (maybe because we have a few
more ilias parsers), it's easy to add back.
