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/notes/search.html.erb

@@ -7,7 +7,7 @@
 
       <%= f.input :body_matches, label: "Body" %>
       <%= f.input :creator_name, label: "Author" %>
-      <%= f.input :post_tags_match, label: "Tags" %>
+      <%= f.input :post_tags_match, label: "Tags", input_html: { data: { autocomplete: "tag-query" } } %>
       <%= f.submit "Search" %>
     <% end %>
   </div>