Add daily supervisions page and form for entering of supervision substitutions

CHANGELOG.rst

aleksis/apps/chronos/filters.py

aleksis/apps/chronos/forms.py

aleksis/apps/chronos/menus.py

...onos/migrations/0012_add_supervision_global_permission.py

aleksis/apps/chronos/models.py

aleksis/apps/chronos/rules.py

aleksis/apps/chronos/tables.py

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

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

aleksis/apps/chronos/urls.py

aleksis/apps/chronos/util/chronos_helpers.py

aleksis/apps/chronos/views.py