Drop large parts of old frontend

aleksis/apps/chronos/admin.py

aleksis/apps/chronos/filters.py

aleksis/apps/chronos/forms.py

aleksis/apps/chronos/models.py

aleksis/apps/chronos/tables.py

aleksis/apps/chronos/templates/chronos/all.html

...sis/apps/chronos/templates/chronos/edit_substitution.html

...onos/templates/chronos/edit_supervision_substitution.html

aleksis/apps/chronos/templates/chronos/lessons_day.html

aleksis/apps/chronos/templates/chronos/my_timetable.html

aleksis/apps/chronos/templates/chronos/substitutions.html

aleksis/apps/chronos/templates/chronos/supervisions_day.html

aleksis/apps/chronos/templates/chronos/timetable.html

aleksis/apps/chronos/templates/chronos/widget.html

aleksis/apps/chronos/urls.py

aleksis/apps/chronos/views.py