[send-share-link] add <a> tag to shared-link in link send email

seahub/templates/shared_link_email.html

@@ -10,7 +10,7 @@
 
 <p style="font-size:14px;color:#434144;">
 {% blocktrans %}{{ email }} shared a {{ file_shared_type }} <span style="font-weight:bold;">{{ file_shared_name}}</span> to you on {{ site_name }}:{% endblocktrans%} <br />
-{{ file_shared_link }}
+<a href="{{ file_shared_link }}">{{ file_shared_link }}</a>
 </p>
 
 {% if extra_msg %}