Allow to specify library or group as remote source in biblatex

[tobiasdiez]

Biblatex supports remote bib files, so we should expose the complete library (or only a group) via a stable endpoint. Usuage would then look like:

\addbibresource[location=remote]{http://www.jabref.org/export/<shared id>?format=biblatex}

The "shared id" should be generated on request and the user needs to keep it safe (workflow should be similar to dropbox/onedrive/... "generate link for sharing").

Reference: https://retorque.re/zotero-better-bibtex/exporting/pull/