fix(a11y): put 'ongoing' after 'end date'

Before this change, the screenreader would simply read "End Date:" and trail off. Now, it will read "End Date: Ongoing". For sighted users, the text is slightly greyed-out to indicate that the end date is not _really_ there (as the project is ongoing).

app/templates/app/project_detail.html

@@ -40,7 +40,13 @@ <h1 id="main-heading">{{ project.name }}</h1>
 
           <p class="col-lg-6">
               {% icon "date" %}
-              {% trans "End Date:" %} {{ project.end_date|date:"Y-m-d" }}
+              {% trans "End Date:" %}
+
+              {% if project.end_date %}
+                {{ project.end_date|date:"Y-m-d"|default:"" }}
+              {% else %}
+                <span class="text-muted">{% trans "ongoing" %}</span>
+              {% endif %}
           </p>
         </div>