Edc

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- add site to SubjectScheduleHistory model (edc-visit-schedule)
- change signature on UnscheduledAppointmentCreator; allow signal
to create unscheduled/interim appointment when using next
appointment CRF based on `allow_create_interim` field value.
(edc-appointment)
- update mixins with `allow_create_interim` field.
(edc-next-appointment)
- allow proxy models but use the proxy_for_model model name to
update and get references (edc-reference).
- add data manager to recipients list (edc-data-manager)
- use title case for "Data Collection Status" app name (edc-metadata)

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- refactor update_skipped_appointments management command
(edc-appointment)
- add SiteModelAdminMixin to SubjectRefusalAdmin to filter by site
(edc-refusal)
- change to use non-ISO numbering (edc-facility)
- fix administration page template failing if app_list is None.
(edc-model-admin)

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- fix issues when setting appointments as skipped, resetting
appointments (edc-appointment, edc-next-appointment)
- (edc-visit-tracking)
- use Django's get_model_related to determine `related_visit` and
other similar properties.
- enforce appointment sequence when saving CRFs in model save.

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- reset migrations. You need to drop the `edc_visit_tracking`
models and delete any migrations under django_migrations
where app="edc_visit_tracking" before running
`migrate`. (edc_visit_tracking)
- add SKIPPED_APPT appointment status; update admin, form classes;
Add settings.EDC_APPOINTMENT_ALLOW_SKIPPED_APPT_USING.
(edc-appointment, edc-next-appointment, edc-visit-tracking)
- minor change to admin (edc-he)

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- fix import and minor typos (edc-crf)
- add custom language internationalization constants (edc-constants)
- refactor SingleSite interface to accept list of `language_codes`
instead of a dict of `languages` (edc-sites)
- NOTE: this is a "breaking" change. Protocol specific sites.py
modules that already declare `languages` will need to be
updated use 'language_codes' instead.

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- add constants (edc-constants)
- use django_apps to get model to prevent circular
import in tests (edc-sites)