Stop using Django's SlugField to avoid conflicting validation

src/pretix/base/migrations/0152_auto_20200510_1042.py

@@ -0,0 +1,35 @@
+# Generated by Django 3.0.6 on 2020-05-10 10:42
+
+from django.db import migrations, models
+import django_countries.fields
+import pretix.helpers.countries
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0151_auto_20200421_0737'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='event',
+            name='slug',
+            field=models.CharField(db_index=True, max_length=50),
+        ),
+        migrations.AlterField(
+            model_name='invoiceaddress',
+            name='country',
+            field=django_countries.fields.CountryField(countries=pretix.helpers.countries.CachedCountries, max_length=2),
+        ),
+        migrations.AlterField(
+            model_name='organizer',
+            name='slug',
+            field=models.CharField(db_index=True, max_length=50, unique=True),
+        ),
+        migrations.AlterField(
+            model_name='seat',
+            name='seat_guid',
+            field=models.CharField(db_index=True, max_length=190),
+        ),
+    ]

src/pretix/base/models/event.py

@@ -287,7 +287,7 @@ class Event(EventMixin, LoggedModel):
         max_length=200,
         verbose_name=_("Event name"),
     )
-    slug = models.SlugField(
+    slug = models.CharField(
         max_length=50, db_index=True,
         help_text=_(
             "Should be short, only contain lowercase letters, numbers, dots, and dashes, and must be unique among your "

src/pretix/base/models/organizer.py

@@ -32,7 +32,7 @@ class Organizer(LoggedModel):
     settings_namespace = 'organizer'
     name = models.CharField(max_length=200,
                             verbose_name=_("Name"))
-    slug = models.SlugField(
+    slug = models.CharField(
         max_length=50, db_index=True,
         help_text=_(
             "Should be short, only contain lowercase letters, numbers, dots, and dashes. Every slug can only be used "