Use common base class for all Archetypes

Created by: marcusfuchs

For #665. From looking at the code, there have been separate base classes for Residential and NonResidential archetypes since 2015, but there was never any need for these to differ. Therefore, I suggest to simplify things into one common Archetype base class. I think that this makes for a clearer starting point to create new archetypes and an easier foundation to understand the currently available ones.

As there were no differences between the two previous base classes, this does not lead to any functional changes.