Show search links in mappings, especially for combined concepts

[nichtich]

Search links can also involve multiple concepts, e.g. https://opac.k10plus.de/DB=2.299/CMD?ACT=SRCHA&IKT=5004&TRM=08.38+and+44.40 for BK 08.37 and 44.40.

These cannot be shown in concept details but in mapping details modal and possibly in mapping editor (as dropdown).

[nichtich]

Might be enough to add an optional field separator so it is backwards-compatible:

For instance searchLinks entry in Cocoda config for BK:

{
      "prefLabel": { "en": "K10plus" },
      "url": "https://opac.k10plus.de/DB=2.299/CMD?ACT=SRCHA&IKT=5004&TRM={notation}",
      "separator": "+and+",
      "schemeUris": [ "http://bartoc.org/en/node/18785" ]
    }

Search links at concept view are unaffected. In addition in mapping details dialog, show search links for one-to-one mappings (always, if schemeUris match) and for one-to-many mappings only if there is a separator. The separator is not URL-encoded to allow for URL patterns with additional query parameters.