Fix #3857: Add searching mod actions by message.

Also allow searching user feedbacks and bulk update requests.

app/views/mod_actions/_search.html.erb

@@ -1,5 +1,6 @@
 <%= simple_form_for(:search, method: :get, url: mod_actions_path, defaults: { required: false }, html: { class: "inline-form" }) do |f| %>
   <%= f.input :creator_name, label: "Creator", input_html: { value: params[:search][:creator_name] } %>
+  <%= f.input :description_matches, label: "Description" %>
   <%= f.input :category, label: "Category", collection: ModAction.categories.map {|k,v| [k.capitalize.tr("_"," "), v]}, include_blank: true,selected: params[:search][:category] %>
   <%= f.submit "Search" %>
 <% end %>