Improve object-URL generation

[saemideluxe]

Since we merged basxsoftwareassociation/bread#138 we can make use of a cleaner API to generate object-URLs inside basxconnect.

This means in most cases to replace something like

href=ModelHref(MyModel, "edit", kwargs={"pk": hg.C("row.pk")})

with something like

href=ModelHref.from_object(hg.C("row"), "edit")