Multiple Version support

[Sveino]

I think that it is very important that we address version support from day-one in our POC. We are not introducing a new concept of having a persistent namespace that support versioning.

GeoSPARQL are starting to find a way of implementing this - we might get inspired by them or even go in dialog. Here are their landing page that support multiple versions, https://opengeospatial.github.io/ogc-geosparql/