Complete cleanup - Githubissues

PR Checklist

[x] Read the contribution guidelines
[ ] Added a brief description of these changes to the top of the changelog
[ ] Changes in code meet test criteria (running mvn test returns exit code 0, without errors)

Do a project-wide cleanup.

Optimize imports
Refactor boilerplate code with Lombok
- Getters + setters
- Default constructors & constructor overloads
- In reality, the only constructors left are @Autowired and copy constructors
Ensure every file complies with the specifications set in the EditorConfig file
Enforce a better naming scheme for classes and methods
- Class and method names should explain roles and purposes from the get-go
- It is preferable to avoid class names over 50 characters long
- Test classes must always be suffixed with Test
- Test methods should be named using underscores_and_lowercase
- Spring component class names should be suffixed with their respective base type name (Service, Controller, Config, Repository)
Write missing unit & integration tests
Make other improvements to the codebase in ways that help to...
- reduce long-remaining bugs
- make the code easier to explore and read, thus to modify, hack or improve too