EPIP: Adapt 5.5 (and eventually 5.6) to the new part 6

[ue71603]

With EPIAP the information in EPIP about accessibility should be reduced to the minimum and mostly contain a reference to part 6.
At least a check for conformance must be made.

[ue71603]

From Christophe: You already can do it thanks to the NoticedObjectRef in NoticeAssignment (that can be a standalone element)... but that's true that this is not explicit and some words about it would help