 RDF to iCalendar converter as a Web Service

### Scala API
```
def graph2iCalendar(graph: Rdf#Graph): String
 ```
### Web Service
It is meant to be widely reusable. The `rdfData` URL can be any URL returning RDF as Turtle, JSON-LD or RDF/XML, subjected to standard content negotiation, as usual in SF. So it can also be a SPARQL endpoint GET URL with a specific query.
```
/icalendar?url=rdfData
```
