Added preview and sections fields to LMS Topic

- The preview is used to show the details of the topic in the course page
- the sections are used to show the different part of the topic, each could be of a different type

Issue #8

community/www/courses/course.html

@@ -32,10 +32,10 @@
 			{% for topic in course.topics %}
 			<div class="list-group-item">
 				<h5><a href="/courses/topic?course={{course.name}}&topic={{topic.name}}">{{topic.title}}</a></h5>
-				<div>{{topic.description}}</div>
+				<div>{{topic.preview | markdown }}</div>
 			</div>
 			{% endfor %}
 		</div>
 	</div>
 </section>
-{% endblock %}
+{% endblock %}