Update RDFlib to 6.1.1 (removed rdflib-jsonld, as it is deprecated)
Bumped minimum python version: 3.7 (as a result of RDFLIB 6)
Added ProxyFix to run behind nginx (Added --no-proxy to run without the fix)
Replaced http media links to protocol-agnostic links in playground
Enable CORS (via --enable-cors)
Update old urls (replaced *.cluster.gsi.dit.upm.es with *.gsi.upm.es)
Kubernetes doesn't pull the `latest` tag automatically, so we need to change the
image tag in the deployment file.
As a plus, we can now see exactly what version we're running.
