Get rid of dependencies in configuration of docker-compose

[blcham]

Relavant part from README:

• RDF4J_SERVER_URL -- to set up different Rdf4j server (defaults to internal docker service at http://rdf4j:8080/rdf4j-server). Note that this variable must be consistent with variable RDF4J_PCONFIGURL.
• RDF4J_REPOSITORYNAME -- to set up different Rdf4j repository name where SPipes logs from execution are created (defaults to s-pipes-hello-world). Note that this variable must be consistent with variable RDF4J_PCONFIGURL.
• RDF4J_PCONFIGURL -- to set up configuration of Rdf4j repository where SPipes logs from execution are created (defaults to $SPIPES_ROOT/doc/examples/hello-world/config.ttl). Note that this variable must be consistent with variables RDF4J_SERVER_URL and RDF4J_REPOSITORYNAME.

[blcham]

Maybe config.ttl would be template with variables?