views: replace .category-N css classes with .tag-type-N

* Replace the .category-N CSS classes on tags with .tag-type-N. Before
  we were inconsistent about whether tag colors were indicated with
  .category-N or .tag-type-N. Now it's always .tag-type-N.

* Fix various places to not use Tag.category_for. Tag.category_for does
  one Redis call per tag lookup, which leads to N Redis calls on many
  pages. This was inefficient because usually we either already had the
  tags from the database, or we could fetch them easily.

app/views/sources/_info.html.erb

@@ -19,7 +19,7 @@
             <% else %>
               (<ul id="source-info-translated-artists">
                 <% @source.artists.each do |artist| %>
-                  <li><%= link_to artist.name, artist_path(artist), class: "tag-type-#{artist.category_name}" %></li>
+                  <li><%= link_to artist.name, artist_path(artist), class: tag_class(artist.tag) %></li>
                 <% end %>
               </ul>)
             <% end %>