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/meta_searches/tags.html.erb

@@ -4,7 +4,7 @@
 
     <section>
       <%= form_tag(meta_searches_tags_path, :method => :get) do %>
-        <%= text_field_tag "name", params[:name] %>
+        <%= text_field_tag "name", params[:name], :data => { :autocomplete => "tag" } %>
         <%= submit_tag "Go" %>
       <% end %>
     </section>
@@ -126,4 +126,4 @@
 
 <% content_for(:page_title) do %>
   MetaSearch - Tags - <%= Danbooru.config.app_name %>
-<% end %>
+<% end %>