refactor: refactored the course page

- simplified the portal page for course
- added mentods to LMS Course and Community Member to reduce custom code
  in portal pages
- included lessons in the ChapterTeaser

community/lms/widgets/ChapterTeaser.html

@@ -4,5 +4,12 @@
     <div class="chapter-description">
       {{ chapter.description or "" }}
     </div>
+    <div class="chapter-lessons">
+      {% for lesson in chapter.get_lessons() %}
+        <div class="lesson-teaser">
+          {{lesson.title}}
+        </div>
+      {% endfor %}
+    </div>
   </div>
 </div>