Upgrade to Django 3.0 and other dependencies (#1568)

* 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

src/pretix/plugins/banktransfer/__init__.py

@@ -1,6 +1,6 @@
 from django.apps import AppConfig
 from django.utils.functional import cached_property
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 
 from pretix import __version__ as version
 

src/pretix/plugins/banktransfer/payment.py

@@ -6,7 +6,7 @@ from django import forms
 from django.core.exceptions import ValidationError
 from django.http import HttpRequest
 from django.template.loader import get_template
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 from i18nfield.fields import I18nFormField, I18nTextarea
 from i18nfield.forms import I18nTextInput
 from i18nfield.strings import LazyI18nString

src/pretix/plugins/banktransfer/signals.py

@@ -1,7 +1,7 @@
 from django.dispatch import receiver
 from django.template.loader import get_template
 from django.urls import resolve, reverse
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 
 from pretix.base.signals import register_payment_providers
 from pretix.control.signals import html_head, nav_event, nav_organizer

src/pretix/plugins/banktransfer/tasks.py

@@ -6,7 +6,7 @@ from celery.exceptions import MaxRetriesExceededError
 from django.conf import settings
 from django.db import transaction
 from django.db.models import Q
-from django.utils.translation import ugettext, ugettext_noop
+from django.utils.translation import gettext, gettext_noop
 from django_scopes import scope, scopes_disabled
 
 from pretix.base.email import get_email_context
@@ -28,7 +28,7 @@ def notify_incomplete_payment(o: Order):
     with language(o.locale):
         email_template = o.event.settings.mail_text_order_expire_warning
         email_context = get_email_context(event=o.event, order=o)
-        email_subject = ugettext('Your order received an incomplete payment: %(code)s') % {'code': o.code}
+        email_subject = gettext('Your order received an incomplete payment: %(code)s') % {'code': o.code}
 
         try:
             o.send_mail(
@@ -96,7 +96,7 @@ def _handle_transaction(trans: BankTransaction, code: str, event: Event=None, or
         trans.state = BankTransaction.STATE_DUPLICATE
     elif trans.order.status == Order.STATUS_CANCELED:
         trans.state = BankTransaction.STATE_ERROR
-        trans.message = ugettext_noop('The order has already been canceled.')
+        trans.message = gettext_noop('The order has already been canceled.')
     else:
         try:
             p, created = trans.order.payments.get_or_create(

src/pretix/plugins/banktransfer/views.py

@@ -12,7 +12,7 @@ from django.shortcuts import get_object_or_404, redirect, render
 from django.urls import reverse
 from django.utils.functional import cached_property
 from django.utils.timezone import now
-from django.utils.translation import ugettext as _
+from django.utils.translation import gettext as _
 from django.views.generic import DetailView, ListView, View
 
 from pretix.base.models import Order, OrderPayment, OrderRefund, Quota