Use a param to trigger export rather than a separate action

In site/_resize.html.erb and site/_search.html.erb, a
params[:action] conditional is used to include code that
should only run on the index action -- but it should be run
on the export action too. Cleanest fix is to eliminate that
action entirely.

app/views/site/index.html.erb

@@ -291,7 +291,7 @@ end
       e.preventDefault();
     });
 
-    <% if params[:action] == 'export' -%>
+    <% if params[:export] -%>
     $("#exportanchor").click();
     <% end -%>