Resolve "Allow editing of subject field on Group model in frontend"

Closes #156 (closed)

aleksis/apps/chronos/form_extensions.py

+from django.utils.translation import gettext as _
+
+from material import Fieldset
+
+from aleksis.core.forms import AnnouncementForm, EditGroupForm
+
+AnnouncementForm.add_node_to_layout(Fieldset(_("Options for timetables"), "show_in_timetables"))
+EditGroupForm.add_node_to_layout(Fieldset(_("Optional data for timetables"), "subject_id"))