Add Literature References

[Scienfitz]

added some literature references where its appropriate but was missing

Ideally we can have last push form everyone to add references in case there are more places where stuff from other work was used or strongly inspired

[AVHopp]

Since I basically only worked on the Naive Hybrid which was not sufficiently inspired by a single reference and on the documentation which is already referenced by the footers in the documentation itself, I do not think that I need to add anything here.