Allow redirect to remote census configuration tab

Currently after each update of any Settings is redirected to the first
tab by default.
As this new tab remote_census_configuation has a lot of fields to fill
in it is a bit uncomfortable to have to go back to the tab after each
update.

- Add hidden field :tag to set current tag value
- After update add tag value to request.referer
- To avoid errors when partial call has not param :tag, add the "define?"
  method on hidden_field value.

app/views/admin/settings/_settings_table.html.erb

@@ -19,7 +19,11 @@
           <% if setting.content_type? %>
             <%= render "admin/settings/content_types_settings_form", setting: setting %>
           <% else %>
-            <%= render "admin/settings/settings_form", setting: setting %>
+            <% if defined?(tab) %>
+              <%= render "admin/settings/settings_form", setting: setting, tab: tab %>
+            <% else %>
+              <%= render "admin/settings/settings_form", setting: setting %>
+            <% end %>
           <% end %>
         </td>
       </tr>