Support changing a type's URI in DMX core
Even if type URIs are not supposed to change there are cases where it makes sense to do so. An example: When you start a plugin that declares types and then later you decide to support a different range of types (e.g. derived from a different standard) you might want/need to change a type URI. My concrete example: I started the biblio plugin inspired my item types from the bibtex standard where there is a distinction between "books" (monographs) and collections. Later, we decided to go with the .ris format that just has books while being much more precise in most other parts. So I would like to change my existing typeURI from dmx.biblio.monograph to dmx.biblio.book.