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

added 4 commits

• 83860693...e37f7f3a - 3 commits from branch master
• 9a0642e7 - Merge remote-tracking branch 'origin/master' into enable_code_coverage

Compare with previous version

added 6 commits

• 9a0642e7...dabbd35f - 5 commits from branch master
• c4974180 - Merge remote-tracking branch 'origin/master' into enable_code_coverage

Compare with previous version

merged

mentioned in commit c16c9f80