BibDocFile: escape file URLs in /files tab

* Escapes file URLs in /files tab.  (closes #2067)

Signed-off-by: Ludmila Marian <ludmila.marian@gmail.com>
Co-authored-by: Jerome Caffaro <jerome.caffaro@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>