Advanced data in timetable views

Closes #72 (closed) Closes #73 (closed)

aleksis/apps/chronos/templates/chronos/partials/subs/badge.html

+{% load i18n %}
+
+{% if sub.cancelled %}
+  <span class="badge new green">{% trans "Cancelled" %}</span>
+{% elif item.el.cancelled_for_teachers %}
+  <span class="badge new green">{% trans "Cancelled for teachers" %}</span>
+{% endif %}