cleanup, use method reference etc.

[robstoll]

some general cleanup suggestions by intellij, spelling fixes and I added some FIXME where the implementation had some unused code where I was not sure whether it was a bug or not

[ltearno]

I am not so much a huge fan of privatizing all those methods and also about changing return types. There are projects out there which use those functions, and they will be break by that change. pom-explorer is one user of pom-explorer-core, but there are others which I don't even control now...

But some parts of your cleaning is very cool...

[robstoll]

Good, I'll revert the private method part as well as removing return types and push another solution

[ltearno]

Thanks, you rock !