modqueue: add order options; change default order to newest first.

* Add options for changing the order of the modqueue (newest first,
  oldest first, highest scoring first, lowest scoring first).

* Change the default order from oldest posts first to most recently
  flagged or uploaded posts first.

* Add an order:modqueue metatag to order by most recently flagged or
  uploaded in standard searches.

app/views/modqueue/_sidebar.html.erb

@@ -3,6 +3,7 @@
 
   <%= search_form_for(modqueue_index_path, classes: "one-line-form") do |f| %>
     <%= f.input :tags, label: false, input_html: { placeholder: "Tags", value: params.dig(:search, :tags), "data-autocomplete": "tag-query" } %>
+    <%= f.input :order, label: false, collection: [["Newest", "modqueue"], ["Oldest", "modqueue_asc"], ["Score (Highest)", "score"], ["Score (Lowest)", "score_asc"]], selected: params[:search][:order] %>
     <%= f.button :button, name: nil, id: "search-box-submit" do %>
       <i class="fas fa-search"></i>
     <% end %>