Get rid of log4j

[m-pavel]

Suggest to replace log4j with slf4j+logback-classic. Better than updating to actual log4j version every week :smile:

[mmarquee]

I will have a look at this after I have upgrade current dependabot log4j changes. I was thinking of simply removing the logging that I am already doing, but that might need some further refactoring.

[pbi-qfs]

Why replacing one external library with another one? I would argue for using the simple logger provided (and bugfixed/maintained) with Java (java.util.logging.Logger), since the complexity of the logging in our library is not that high and you can easily bridge the java logger into another more powerful framework, if needed.

[pbi-qfs]

That would look like #130