Some dependencies are not available for python 3.7 anymore. Instead
of trying to support different versions of the libraries, we opt to
focus on the latest python version, and allow for CORE functionality
for earlier versions.
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)
pip install needs the VERSION file - `make version` will create that file
I also added the -U flag to pip install to force install (this is important if the user is playing with the code or trying out different older versions, as pip will not install if it thinks the git repo represents a version already installed or older than the one installed)
