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
Should be:

```scala
extends Jsonp(paramName) {
```

(not sure for `codec` and `ex` params)

BTW I don’t like having this `JsonpJava` class. I’d rather have a convenient factory method for Java users in the `Jsonp` companion object.