Migration to Play 2.3

Change Scala and Play versions
Use play.api.mvc.Result instead of SimpleResult
Add special class with no args constructor to support Java
Oh, you are right. (BTW I don’t understand this design choice for the Java filters API)

You can add a no args constructor in `Jsonp.scala` as follows:

```scala
def this() = this(Jsonp.DefaultParamName)(utf_8, defaultContext)
```