css: ensure dtext is always wrapped in .prose container.

Ensure dtext is always wrapped in a `<div class="prose">` or
`<span class="prose">` (for inline dtext) container so that dtext css is
properly applied.

app/views/bans/show.html.erb

@@ -4,7 +4,12 @@
     <ul style="margin-bottom: 1em;">
       <li><strong>User</strong>: <%= link_to_user(@ban.user) %></li>
       <li><strong>Expires</strong>: <%= compact_time @ban.expires_at %></li>
-      <li><strong>Reason</strong>: <%= format_text @ban.reason %></li>
+      <li>
+        <strong>Reason</strong>:
+        <div class="prose">
+          <%= format_text @ban.reason %>
+        </div>
+      </li>
     </ul>
 
     <%= form_tag(ban_path(@ban), :method => :delete) do %>