feat(pub): Only generate Cite button when cite.bib is present

Enables users to place other *.bib files in the folder, to be used for
other purposes such as Blogdown bibliographies.

Close #1157

layouts/partials/page_links.html

@@ -29,7 +29,7 @@
   {{ i18n "btn_pdf" }}
 </a>
 {{ end }}
-{{ $resource := $page.Resources.GetMatch "*.bib" }}
+{{ $resource := $page.Resources.GetMatch "cite.bib" }}
 {{ with $resource }}
 <button type="button" class="btn btn-outline-primary my-1 mr-1{{ if $is_list }} btn-sm{{end}} js-cite-modal"
         data-filename="{{ .RelPermalink }}">

layouts/partials/page_links_div.html

@@ -10,7 +10,7 @@
   {{ $pdf_link = true }}
 {{ end }}
 
-{{ $resource := $page.Resources.GetMatch "*.bib" }}
+{{ $resource := $page.Resources.GetMatch "cite.bib" }}
 {{ with $resource }}
   {{ $cite_link = true }}
 {{ end }}