Add same logic as for Connector and generate flattened concepts once per URI instead of 4 times per URI

Here are some changes please review them. The first part implements the same logic we currently have in the SPHN Connector to extract restrictions. This should be handling the third level owl:someValuesFrom that appears in the new schema. Nevertheless, I'm not sure if that's really needed for the SPARQL statistics query generation. Maybe it could be re-used as hint for the changes needed for the HTML generation. The second part of the changes basically just extract the concept flattening at the higher level such that it is not generated for every template (I also spotted some inconsistencies in the generation when run multiple times for the templates).