* sendmail: allow to attach files to emails
* Fix mixup of model objects and model IDs
* Attach to order-level emails, not only position-level emails
* Give attachments a proper file type
* Add a warning note about higher spam chances
Co-authored-by: Raphael Michel <mail@raphaelmichel.de>
* Upgrade Django to 3.0 and other dependencies to recent versions
* Fix otp version contsraint
* Remove six dependency
* Resolve some warnings
* Fix failing tests
* Update django-countries
* Resolve all RemovedInDjango31Warnings in test suite
* Run isort
* Fix import
* Update PostgreSQL version on travis
* .
* Add a position detail page to the frontend
* Mail templates
* Send mails
* Send reminder email
* Add position support to sendmail plugin
* Add and fix some tests
* Fix failing test on real databases
- [x] Provide data model and configuration toggle
- [x] Allow to delete individual test orders
- [x] Add tests
- [x] Add a prominent warning message to the backend if test mode orders exist (even though test mode is off), as this leads to wrong statistics
- [x] Decide if and how to generate invoices for test orders as invoice numbers cannot be repeated or should not have gaps.
- [x] Decide if and how we expose test orders through the API, since our difference pull mechanism relies on the fact that orders cannot be deleted.
- [x] Decide if and how we want to couple test modes of payment providers?
- [ ] pretix.eu: Ignore test orders for billing
- [ ] Adjust payment providers: Mollie, bitpay, cash, fakepayment, sepadebit

* Custom HTML email renderers
* Move inline_css call
* Small fixes
* New HTML mail style for pretix
* Thumbs
* Inlinestyle for notifications
* Documentation
* Set line-height