Add references/dois/bibliography

[kmuehlbauer]

As a almost static page we could also think about adding citations and references to papers, conference contributions and the like

This could be handled under a heading for each package/project (for package/project related references/citings).

For an overall view we can add kind of bibliography page or add a section to the references. Or even rename References to Downloads?

This isn't much of a maintenance burden beside adding new entries when they appear.