publication widget: Add option to exclude selected publications

Add `exclude_selected = false` option to frontmatter of publication
widget.

See #385

exampleSite/content/home/publications.md

@@ -31,5 +31,8 @@ list_format = 3
 #  5: Book
 #  6: Book chapter
 publication_type = "-1"
+
+# Exclude publications that are shown in the Selected Publications widget?
+exclude_selected = false
 +++
 

layouts/partials/widgets/publications.html

@@ -25,6 +25,10 @@
       {{ $.Scratch.Set "recent_pubs" (where $.Site.RegularPages "Type" "publication") }}
     {{ end }}
 
+    {{ if $page.Params.exclude_selected }}
+      {{ $.Scratch.Set "recent_pubs" ( ($.Scratch.Get "recent_pubs") | intersect (where (where $.Site.RegularPages "Type" "publication") ".Params.selected" "!=" true) ) }}
+    {{ end }}
+
     {{ $recent_pubs := $.Scratch.Get "recent_pubs" }}
     {{ range first $page.Params.count $recent_pubs }}
       {{ if eq $page.Params.list_format 1 }}