LibreOffice integration should support bst files

[koppor]

There was an initial support for bst in the LibreOffice integration, but it was unfinished (see #602 (comment)). Therefore, it got removed in #602.

Since bst is still used by many publishers, although CitationStyles (#119) gain popularity.

Maybe, pandoc can be used to convert the latex output into HTML (refs #602 (comment)).