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/control/forms/__init__.py

@@ -6,7 +6,7 @@ from django.conf import settings
 from django.core.exceptions import ValidationError
 from django.core.files import File
 from django.forms.utils import from_current_timezone
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 
 from ...base.forms import I18nModelForm
 # Import for backwards compatibility with okd import paths

src/pretix/control/forms/event.py

@@ -10,7 +10,7 @@ from django.urls import reverse
 from django.utils.html import escape
 from django.utils.safestring import mark_safe
 from django.utils.timezone import get_current_timezone_name
-from django.utils.translation import pgettext_lazy, ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _, pgettext_lazy
 from django_countries import Countries
 from django_countries.fields import LazyTypedChoiceField
 from i18nfield.forms import (

src/pretix/control/forms/filter.py

@@ -8,7 +8,7 @@ from django.db.models.functions import Coalesce, ExtractWeekDay
 from django.urls import reverse, reverse_lazy
 from django.utils.functional import cached_property
 from django.utils.timezone import get_current_timezone, make_aware, now
-from django.utils.translation import pgettext_lazy, ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _, pgettext_lazy
 
 from pretix.base.forms.widgets import DatePickerWidget
 from pretix.base.models import (

src/pretix/control/forms/global_settings.py

@@ -1,7 +1,7 @@
 from collections import OrderedDict
 
 from django import forms
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 from i18nfield.forms import I18nFormField, I18nTextarea, I18nTextInput
 
 from pretix.base.forms import SettingsForm

src/pretix/control/forms/item.py

@@ -7,7 +7,7 @@ from django.db.models import Max
 from django.forms.formsets import DELETION_FIELD_NAME
 from django.urls import reverse
 from django.utils.translation import (
-    pgettext_lazy, ugettext as __, ugettext_lazy as _,
+    gettext as __, gettext_lazy as _, pgettext_lazy,
 )
 from django_scopes.forms import (
     SafeModelChoiceField, SafeModelMultipleChoiceField,

src/pretix/control/forms/orders.py

@@ -8,7 +8,7 @@ from django.db import models
 from django.urls import reverse
 from django.utils.timezone import make_aware, now
 from django.utils.translation import (
-    gettext_noop, pgettext_lazy, ugettext_lazy as _,
+    gettext_lazy as _, gettext_noop, pgettext_lazy,
 )
 from i18nfield.forms import I18nFormField, I18nTextarea, I18nTextInput
 from i18nfield.strings import LazyI18nString

src/pretix/control/forms/organizer.py

@@ -7,7 +7,7 @@ from django.core.exceptions import ValidationError
 from django.core.validators import RegexValidator
 from django.db.models import Q
 from django.utils.safestring import mark_safe
-from django.utils.translation import pgettext_lazy, ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _, pgettext_lazy
 from django_scopes.forms import SafeModelMultipleChoiceField
 from i18nfield.forms import I18nFormField, I18nTextarea
 

src/pretix/control/forms/subevents.py

@@ -7,7 +7,7 @@ from django.urls import reverse
 from django.utils.dates import MONTHS, WEEKDAYS
 from django.utils.functional import cached_property
 from django.utils.timezone import now
-from django.utils.translation import pgettext_lazy, ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _, pgettext_lazy
 from i18nfield.forms import I18nInlineFormSet
 
 from pretix.base.forms import I18nModelForm

src/pretix/control/forms/users.py

@@ -4,7 +4,7 @@ from django.contrib.auth.password_validation import (
     password_validators_help_texts, validate_password,
 )
 from django.db.models import Q
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 from pytz import common_timezones
 
 from pretix.base.models import User

src/pretix/control/forms/vouchers.py

@@ -7,7 +7,7 @@ from django.core.exceptions import ObjectDoesNotExist, ValidationError
 from django.core.validators import EmailValidator
 from django.db.models.functions import Lower
 from django.urls import reverse
-from django.utils.translation import pgettext_lazy, ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _, pgettext_lazy
 from django_scopes.forms import SafeModelChoiceField
 
 from pretix.base.email import get_available_placeholders