添加站内消息，修复讨论节点丢失的问题

templates/user_detail.html

@@ -9,7 +9,7 @@
         <div class="profile-header__content">
           <div class="media">
             <div class="media__left">
-              <img src="{{ udoc.gravatar|gravatar_url }}" width="120" height="120" class="large user-profile-avatar">
+              <img src="{{ gravatar(udoc.gravatar) }}" width="120" height="120" class="large user-profile-avatar">
             </div>
             <div class="media__body profile-header__main">
               <h1>