json-ld for sesame. 

Added JSON-LD for Sesame, by re-adapting the PR by @artemkozlov in  https://github.com/w3c/banana-rdf/pull/61 to the current code. This is not to abandon the use of Semargl as described by issue #67 , which I would like to do later - after I have finished getting rww-play to pass the LDP tests.
You can use pattern matching for more safety:

```scala
scala> "foo:bar".split(':') match { case Array(f, b) => true; case _ => false }
res1: Boolean = true
```