Use common base class for all Archetypes

[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.

[coveralls]

Coverage increased (+0.006%) to 88.997% when pulling ff213d5293f204d1c5a2995a03bc3481d453bcab on marcusfuchs:issue665_baseclass into c2ded844a7f5c73c53c7ecc9238c27bc205ece41 on RWTH-EBC:development.

[PRemmen]

I'll transfer it to a teaser branch to get CI running and then merge if there are not tests failing