LaTeX template: added natbiboptions variable.

Closes #3768.

MANUAL.txt

@@ -1462,6 +1462,9 @@ LaTeX variables are used when [creating a PDF].
 `biblatexoptions`
 :   list of options for biblatex.
 
+`natbiboptions`
+:   list of options for natbib.
+
 [`article`]: https://ctan.org/pkg/article
 [`report`]: https://ctan.org/pkg/report
 [`book`]: https://ctan.org/pkg/book

data/templates/default.latex

@@ -113,7 +113,7 @@ $if(geometry)$
 \usepackage[$for(geometry)$$geometry$$sep$,$endfor$]{geometry}
 $endif$
 $if(natbib)$
-\usepackage{natbib}
+\usepackage[$natbiboptions$]{natbib}
 \bibliographystyle{$if(biblio-style)$$biblio-style$$else$plainnat$endif$}
 $endif$
 $if(biblatex)$