locality literature links

[ollehints]

locality literature table should include url and pdf icons from the index so that a user can quickly open the reference in a popup window - currently, it is not evident that many references are easily accessible online.
example: https://geoloogia.info/locality/12431/vasalemma-karjaar

[Erikdzo]

Currently the references come from REST api locality_reference endpoint, not from the Solr reference index. Therefore adding the links is quite more difficult. The REST endpoint contains locality reference remarks which are not present Solr index, as they live separately in the LocalityReference model not in the Reference model.

With the current implementation we can only the url icon link, as it is the only on that is defined in the Reference model. The pdf link and book pdf link are added by the solr index.

Any ideas how we could solve this problem?