add basic support for labels

app/views/forumthreads/show.html.erb

@@ -1,5 +1,5 @@
 <%= link_to @thread.forum.group, forumgroup_path(@thread.forum.group) %> → <%= link_to @thread.forum, @thread.forum %> → <%=truncate(@thread.title, length: 60, omission: " …") %>
-<h1><%= title @thread.title %></h1>
+<h1><%= render partial: "labels/label", locals: {label: @thread.label} %><%= title @thread.title %></h1>
 
 <div class="item-group thread with-avatar" id="thread-<%= @thread.id %>">
   <div class="header">

app/views/labels/_label.html.erb

@@ -0,0 +1,3 @@
+<% if label %>
+  <span class="label label-<%= label.name.downcase %>"><%= label %></span>
+<% end %>