provide a new data/ontologies.json

[mpo-vliz]

now that the /ns repo is getting there, we should be able to list the ontologies we use as part of our "space" too

obiously this will need to be matched by some updates to our spaces-to-pages action

for these ontologies there should be

• a new section on the home page, linking to them
• a menu section to scoll down to that section
• some exposure in the metadata.ttl for the space listing them as well -- check with @laurianvm for appropriate triples to use

[laurianvm]

@cedricdcc let me know when you want to have a look at this :)