Enable code coverage
This PR introduces code coverage support to the project
after a
mvn clean install
the code coverage report is in StorSimCore.test/target/site/jacoco-aggregate
Additionally, gitlab is supposed to show to coverage information in the Pull Request (never tested let's see if it works) https://docs.gitlab.com/ee/user/project/merge_requests/test_coverage_visualization.html
The Pr also improves a little bit the README.md