feat(widget): enable splitting Talks section into past and upcoming talks

See #721

exampleSite/content/home/talks.md

@@ -28,7 +28,9 @@ subtitle = ""
     category = ""
     publication_type = ""
     exclude_featured = false
-  
+    exclude_past = false
+    exclude_future = false
+    
 [design]
   # Toggle between the various page layout types.
   #   1 = List

layouts/partials/widgets/pages.html

@@ -33,6 +33,12 @@
 {{ if $st.Params.content.filters.exclude_featured }}
   {{ $query = where $query "Params.featured" "!=" true }}
 {{ end }}
+{{ if $st.Params.content.filters.exclude_past }}
+  {{ $query = where $query "Date" "<=" now }}
+{{ end }}
+{{ if $st.Params.content.filters.exclude_future }}
+  {{ $query = where $query "Date" ">" now }}
+{{ end }}
 
 {{/* Sort (use Hugo default for now) */}}
 {{/* $sort_by := "Date" */}}