Fix broken tag autocomplete on multiple pages.

Mark all tag <input>s with a `data-autocomplete` attribute, instead of
hardcoding a list of html IDs to autocomplete in javascript.

This way should be less error prone. It fixes autocomplete in several places:

* Autocomplete for the search box on /posts didn't work in the
  responsive layout. This was because /posts has two search boxes that
  both have the id `tags`: one in the normal sidebar, and one in the
  responsive tag list. $("#tags") only initialized autocomplete on the
  first one.

* Autocomplete didn't work on the aliases or implications pages. This
  was due to selecting the wrong html ids.

app/views/moderator/post/queues/show.html.erb

@@ -5,7 +5,7 @@
 
       <div id="search">
         <%= form_tag(moderator_post_queue_path, :method => :get) do %>
-          <%= text_field_tag "query", params[:query], :size => 40 %>
+          <%= text_field_tag "query", params[:query], :size => 40, :data => { :autocomplete => "tag-query" } %>
           <%= select_tag "per_page", options_for_select(%w(25 50 100 200), cookies["mq_per_page"])%>
           <%= submit_tag "Search" %>
         <% end %>