Scala test fw

First attempt to use the inhouse Scala testing framework with one test for checking the picture overlay functionality. Keep in mind that I am a beginner Scala dev so code will likely look very "Javaish"
Consts in Scala should use capitalised camel-style:

```scala
val InPicturesContainerId = "in-pictures"
```

See http://docs.scala-lang.org/style/naming-conventions.html#values_variable_and_methods