Unifiy backend tree structure

[heliocastro]

Code-wise, SW360 backend is cluttered with multiple subfolders, separating the library modules from the tomcat servlet code, making maintenance complex.

The idea is to eliminate backend/src/src-, backend/svc/svc-module and common properties and unify them in a single structure under backend.

An initial layout branch exists already and all the base maven structure is rearranged to a cleaner view.

Some issues need to be resolved. Modules like projects and vulnerabilities are used as both servlets and as a library themselves. This will force a split between the servlet and the shared library code.

The opportunity to execute this refactor arises now since we are cleaning SW360 codebase.

[GMishx]

Since we do not have liferay in picture anymore, I also agree with unifying the libraries. What are your opinions on this @smrutis1 ?

[KoukiHama]

I fully support this refactor. Simplifying the backend structure will greatly improve maintainability and make future development more efficient.