Fetch OPAC URL templates from source file

[acka47]

Currently, we replicate the file https://github.com/hbz/link-templates/blob/master/isil2opac_hbzid.json both in this repo and in the NWBib repo. As this file needs to be updated quite often, this is impractical. In the future, OPAC URL templates should directly be fetched from GitHub at https://raw.githubusercontent.com/hbz/link-templates/master/isil2opac_hbzid.json.

[TobiasNx]

@acka47 still relevant for ALMA?

[dr0i]

With #1902 we use gitsubmodules so lookup table is updated automatically.
Closing.