BibFormat: additional fulltext file display in HB

* Improves display of Additional files in the default HB format
  displaying the link "(additional files)".  (closes #1219)

Reported-by: Devin Bougie <devin.bougie@cornell.edu>
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>
Merge branch 'maint-1.0' into maint-1.1

* maint-1.0:
  BibFormat: additional fulltext file display in HB