Merge branch 'issue29' into 'master'

Save selections in URL. Closes #29.

Closes #29

See merge request Teckids/BiscuIT/BiscuIT-App-Chronos!12

biscuit/apps/chronos/templates/chronos/tt_week.html

@@ -18,10 +18,10 @@
       <h1>{{ day }}</h1>
     </div>
     <div class="btn-group" role="group" aria-label="Day actions">
-      <a href="{% url 'timetable_by_week' week_prev %}" class="btn btn-secondary">
+      <a href="{% url 'timetable_by_week' week_prev %}?{{ request.GET.urlencode }}" class="btn btn-secondary">
         {% fa 'arrow-left' %}
       </a>
-      <a href="{% url 'timetable_by_week' week_next %}" class="btn btn-secondary">
+      <a href="{% url 'timetable_by_week' week_next %}?{{ request.GET.urlencode }}" class="btn btn-secondary">
         {% fa 'arrow-right' %}
       </a>
     </div>