cei:repository/cei:arch performing double duty as analogue to tei:institution and tei:respository

Created by: larkvi

The files undergoing TEI conversion are receiving stricter checks on duplicate elements in cei:archIdentifier, which revelas that in many cases the lack of a cei:institution (as envisioned on the CEI tag list) is being accomodated by duplicating either cei:arch or cei:repository, as in this example, from IlluminierteUrkunden/1333-12-20_Freiberg-Sachsen:

                        <cei:archIdentifier>
                            <cei:settlement>Freiberg (Sachsen)</cei:settlement>
                            <cei:arch>Rathaus</cei:arch>
                            <cei:arch>Ratsarchiv</cei:arch>
                        </cei:archIdentifier>

I propose to create a cei:institution element, identical to cei:repository but for the name, and add it to cei:archIdentifier and cei:altIdentifier in order to facilitate cleaning the data in order to avoid collisions on restricted elements, and facilitate the use case that the data and users clearly need to represent the diffference between archives and the institutions housing them.