Create UML diagrams to present overview and relation between classes

[lcomet]

It will be useful to have UML type diagrams to represent the classes of the model and their relationships, as well as the attributes of each class. For example, to have a better overview in the analysis of the model for the discussion for Guide v2
As a reference, look at the DCAT example here
This is necessary to have a general idea of the model, beyond the visualisation of the ontology via WebOWL.

Initial work here