Spit information standard per zib release and major FHIR version and update homepage

[MariekeMassa]

The information standard will be split in the zib2017/stu3 and zib2020/r4 version. The IG's are already separate, but we need to check if the texts and references are still correct.

[HarmkeKoning]

I checked all pages and we only discuss STU3 vs R4 on the data exchange page. So we need to look into that page specifically.

[MariekeMassa]

I checked all pages and we only discuss STU3 vs R4 on the data exchange page. So we need to look into that page specifically.

Indeed, I think it would be best to just talk about two distinct transactions and completely leave out STU3 on the data exchange page. Acknowledging the existence of STU3 is maybe something for the homepage?