Upgrade to Django 2.2 and modern DRF and py.test (#1246)

* Upgrade django and stuff

* Update to Django 2.2 and recent versions of similar packages

* Provide explicit orderings to all models used in paginated queries

* Resolve naive datetime warnings in test suite

* Deal with deprecation warnings

* Fix sqlparse version

src/pretix/plugins/badges/models.py

@@ -52,3 +52,6 @@ class BadgeItem(models.Model):
                                 on_delete=models.CASCADE)
     layout = models.ForeignKey('BadgeLayout', on_delete=models.CASCADE, related_name='item_assignments',
                                null=True, blank=True)
+
+    class Meta:
+        ordering = ('id',)

src/pretix/plugins/banktransfer/models.py

@@ -21,6 +21,9 @@ class BankImportJob(models.Model):
     created = models.DateTimeField(auto_now_add=True)
     state = models.CharField(max_length=32, choices=STATES, default=STATE_PENDING)
 
+    class Meta:
+        ordering = ('id',)
+
     @property
     def owner_kwargs(self):
         if self.event:
@@ -76,3 +79,4 @@ class BankTransaction(models.Model):
 
     class Meta:
         unique_together = ('event', 'organizer', 'checksum')
+        ordering = ('date', 'id')

src/pretix/plugins/ticketoutputpdf/models.py

@@ -73,3 +73,4 @@ class TicketLayoutItem(models.Model):
 
     class Meta:
         unique_together = (('item', 'layout', 'sales_channel'),)
+        ordering = ("id",)