Add posters to the research bibliography

[juliajbeine]

As discussed in dracor-org/dracor-frontend#355, we may consider adding DraCor-related posters to the research bibliography. Currently, this would pertain to the 4 posters on the posters website and the 9 posters in the Zenodo community.

[lehkost]

I added two posters including the marker "[Poster contribution.]", see here – so we can always distinguish what's a poster (in case of bibliographic analysis where we want to separate posters from papers, etc.). Is that a viable way forward?

[juliajbeine]

@lehkost, I think that the marker is a good idea. So, we always add the marker directly after the title and before the BoA title, volume, place, etc., right?