Add user management options

[labra]

We should consider the possibility that users of RDFShape can login to the application so they can store shapes, RDF data, SPARQL queries and so on. In this way, the UI experience would increase.

One drawback is that the complexity of RDFShape would increase as it would require a dependency on a database. However, the benefits can be great and we could track better the differente usages of the application.

Another possibility is that users can algo delegate their credentials to RDFShape allowing them to author shapes/entity schemas inside RDFShape and store them in Wikibases.