Adapt substitution PDF to new data model

aleksis/apps/chronos/models.py

aleksis/apps/chronos/templates/chronos/partials/rooms.html

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

.../apps/chronos/templates/chronos/partials/subs/colour.html

.../apps/chronos/templates/chronos/partials/subs/groups.html

.../apps/chronos/templates/chronos/partials/subs/period.html

...is/apps/chronos/templates/chronos/partials/subs/room.html

...s/apps/chronos/templates/chronos/partials/subs/rooms.html

...apps/chronos/templates/chronos/partials/subs/subject.html

...pps/chronos/templates/chronos/partials/subs/teachers.html

...s/apps/chronos/templates/chronos/substitutions_print.html

aleksis/apps/chronos/util/build.py

aleksis/apps/chronos/util/chronos_helpers.py

aleksis/apps/chronos/views.py