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/presenters/tag_set_presenter.rb

@@ -107,7 +107,7 @@ class TagSetPresenter < Presenter
     count = tag.post_count
     category = tag.category
 
-    html = %{<li class="category-#{tag.category}">}
+    html = %{<li class="tag-type-#{tag.category}">}
 
     unless name_only
       if category == Tag.categories.artist