feat: added get_profile_url function to get the profile url in templates

This takes care of generating the correct profile URL depending on the
`profile_url_prefix` setting.

Issue #192

community/lms/widgets/MemberCard.html

@@ -11,5 +11,5 @@
     Created {{ course_count }} {{ suffix }}
   </div>
   {% endif %}
-  <a class="stretched-link" href="/user/{{ member.username }}"></a>
+  <a class="stretched-link" href="{{ get_profile_url(member.username) }}"></a>
 </div>