Moved CI helper scripts to "Tools/ContinuousIntegration" and enabled Java assertions in POM files and helper scripts.

.gitlab-ci.yml:
- Refactored complete file: moved comment on top of file.
- Call helper scripts in "Tools/ContinuousIntegration" instead of just "Tools".

Tools/ContinuousIntegration/run_vadere_console_with_all_scenario_files.py:
- Execute scenario files alphabetically.
- Use "-enableassertions" when invoking Java.

POM files:
- Use "<enableAssertions>true</enableAssertions>" to be independent of SureFire's default settings.

.gitlab-ci.yml:
- Use "mvn <options> <phase>" syntax consequently like mentioned in "mvn --help".