Enable Continous Integration and junit 5 test suite
This Pull request:
- enable the continuous integration of the project usiong gitlab pipeline (cf. https://gitlab.inria.fr/adt-mochy/mochy/-/pipelines)
- move StorSimCore/src folder to src/main/java in order to follow maven conventions
- add a simple test suite for StorSimCore
- archive tests on the CI (ex: https://gitlab.inria.fr/adt-mochy/mochy/-/pipelines/178566/test_report (ie. you can access this kind of link from the pipelien view, then click on passed or failed then click on the "Tests" tab)