Change how we display identifiers

[ManonGros]

As pointed out in this issue: #158

We have too many identifiers and they can be quite confusing.
On each collection/institution page, I would like to have a "how to cite" box with the preferred identifier or the entry URL (if no preferred identifier is provided).

The other identifiers should either be displayed in a collapsable manner or we could also just consider putting a link to the identifier page of the related registry entry.

@MortenHofft would that work?