Refactors order_selector

Moves the information about the current order to the selector, not to
the container

app/views/shared/_order_selector.html.erb

@@ -0,0 +1,15 @@
+<% # Params:
+   #
+   #   i18n_namespace: for example "moderation.debates.index"
+%>
+
+<form class="inline-block">
+  <select class="js-location-changer js-order-selector" data-order="<%= @current_order %>" name="order-selector">
+     <% @valid_orders.each do |order| %>
+       <option <%= 'selected' if order == @current_order %>
+               value='<%= current_path_with_query_params(order: order, page: 1) %>'>
+         <%= t("#{i18n_namespace}.orders.#{order}") %>
+       </option>
+     <% end %>
+   </select>
+</form>