Add two new learning tests and extends readme file.

Add two new learning test diversify the observer approach. The readme
file describe this.
Close #2: Methoden für Setzen und Änderung eines Werts

Introduce tow methods in Slot1: valueUpdated() and valueChanged().
Change from 3-clause BSD to 2-clause BSD.
Close #3: Maven konfigurieren für Release

Complete Maven configuration include checkstyle, report etc. Clean up
main source code to satisfy checkstyle