Testing with a local instance of revenj

called with `sbt test`.

This PR also reverts CustomDefaultScalaModule removal in json deserialization module.
 
Expects a database with database name, role and its password 'scalaclienttest' and mono installed.

Jar generated from `scalatest.dsl` is added to the test classpath on load.

On test call revenj server is generated if not already present in `http/revenj`.
The test task will try to run it before starting tests.
This instance of revenj can be replaced with other, maybe, debug instance.
In this case task will throw errors instead of starting revenj, but will continue testing all the same.