Improve code quality on the main branch

[CSchoel]

• After SonarQube and/or LGTM have been set up (Set up a tool that produces code quality metrics and reports code smells #98), fix all high severity issues that the tools report on the main branch
• Also go through all lower severity issues and decide whether they need to be fixed
  • If possible, you can disable warnings for irrelevant issues, but you should be able to defend this decision with solid arguments.
• Keep watch over all pull requests to the main branch, ensuring that no new high severity issues are introduced

[CptKaNe]

Today I started improving the code quality. Therefore i created a new branch named codequality out of the main branch and had a look at the critical and major issues listed from sonarqube. However, I am insecure about the issues concerning the System.out.println() statements. Sonarqube wants us to replace these with a logger, but due to our consoleapplication this cannot be the right way i guess, so can we Ignore this issues?

In Addition to that @manuEbg & @IlmarB we should check that you are not working on code while I am about to refactor that so that we dont work against each other on these code fragments.