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.
The tests pass, so this is the way it is currently working. Do you want to change the implementations?

It is also the way the java.net.URI functions.

```
$ scala
Welcome to Scala version 2.10.3 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_67).
Type in expressions to have them evaluated.
Type :help for more information.

scala> import java.net.URI
import java.net.URI

scala> new URI("http://example.com/ldpc")
res0: java.net.URI = http://example.com/ldpc

scala> val u = new URI("http://example.com/ldpc")
u: java.net.URI = http://example.com/ldpc

scala> u.relativize(new URI("http://example.com/ldpc/"))
res1: java.net.URI = 

scala> u.relativize(new URI("http://example.com/ldpc"))
res2: java.net.URI =

scala> u.relativize(new URI("http://example.com/ldpc/entry"))
res3: java.net.URI = entry
```