Add sub-events and relative date settings (#503)

* Data model

* little crud

* SubEventItemForm etc

* Drop SubEventItem.active, quota editor

* Fix failing tests

* First frontend stuff

* Addons form stuff

* Quota calculation

* net price display on EventIndex

* Add tests, solve some bugs

* Correct quota selection in more places, consolidate pricing logic

* Fix failing quota tests

* Fix TypeError

* Add tests for checkout

* Fixed a bug in QuotaForm

* Prevent immutable cart if a quota was removed from an item

* Add tests for pricing

* Handle waiting list

* Filter in check-in list

* Fixed import lost in rebase

* Fix waiting list widget

* Voucher management

* Voucher redemption

* Fix broken tests

* Add subevents to OrderChangeManager

* Create a subevent during event creation

* Fix bulk voucher creation

* Introduce subevent.active

* Copy from for subevents

* Show active in list

* ICal download for subevents

* Check start and end of presale

* Failing tests / show cart logic

* Test

* Rebase migrations

* REST API integration of sub-events

* Integrate quota calculation into the traditional quota form

* Make subevent argument to add_position optional

* Log-display foo

* pretixdroid and subevents

* Filter by subevent

* Add more tests

* Some mor tests

* Rebase fixes

* More tests

* Relative dates

* Restrict selection in relative datetime widgets

* Filter subevent list

* Re-label has_subevents

* Rebase fixes, subevents in calendar view

* Performance and caching issues

* Refactor calendar templates

* Permission tests

* Calendar fixes and month selection

* subevent selection

* Rename subevents to dates

* Add tests for calendar views

src/pretix/control/views/main.py

@@ -90,6 +90,7 @@ class EventWizard(SessionWizardView):
             event = form_dict['basics'].instance
             event.organizer = foundation_data['organizer']
             event.plugins = settings.PRETIX_PLUGINS_DEFAULT
+            event.has_subevents = foundation_data['has_subevents']
             form_dict['basics'].save()
 
             has_control_rights = self.request.user.teams.filter(
@@ -106,6 +107,17 @@ class EventWizard(SessionWizardView):
                 t.members.add(self.request.user)
                 t.limit_events.add(event)
 
+            if event.has_subevents:
+                event.subevents.create(
+                    name=event.name,
+                    date_from=event.date_from,
+                    date_to=event.date_to,
+                    presale_start=event.presale_start,
+                    presale_end=event.presale_end,
+                    location=event.location,
+                    active=True
+                )
+
             logdata = {}
             for f in form_list:
                 logdata.update({