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"
Doesn't really matter, but just FYI there's a nicer way to do `String` interpolation:

```scala
s"${frontsBaseUrl}/preference/platform/mobile?page=${url}&view=mobile"
```

It's shorter to type, and I personally find it a little easier to read. But also in the background it's using a `StringBuilder`, so it's actually more efficient, too ...