Fix #774 -- Make question options sortable (#786)

* add position field

* add question option sorting logic
* add meta class to question option for sorting
* regenerate migration
* add template content and view mechanics

* Rename migration after rebase & update dependency

src/pretix/base/migrations/0084_questionoption_position.py

@@ -0,0 +1,41 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.9 on 2018-03-03 16:41
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+def set_position(apps, schema_editor):
+    Question = apps.get_model('pretixbase', 'Question')
+    for q in Question.objects.all():
+        for i, option in enumerate(q.options.all()):
+            option.position = i
+            option.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0083_auto_20180228_2102'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='questionoption',
+            options={'ordering': ('position', 'id'), 'verbose_name': 'Question option', 'verbose_name_plural': 'Question options'},
+        ),
+        migrations.AddField(
+            model_name='questionoption',
+            name='position',
+            field=models.IntegerField(default=0),
+        ),
+        migrations.AlterField(
+            model_name='question',
+            name='position',
+            field=models.PositiveIntegerField(default=0, verbose_name='Position'),
+        ),
+        migrations.RunPython(
+            set_position, 
+            reverse_code=migrations.RunPython.noop,
+        ),
+    ]

src/pretix/base/models/items.py

@@ -682,8 +682,9 @@ class Question(LoggedModel):
         blank=True,
         help_text=_('This question will be asked to buyers of the selected products')
     )
-    position = models.IntegerField(
-        default=0
+    position = models.PositiveIntegerField(
+        default=0,
+        verbose_name=_("Position")
     )
     ask_during_checkin = models.BooleanField(
         verbose_name=_('Ask during check-in instead of in the ticket buying process'),
@@ -779,10 +780,16 @@ class Question(LoggedModel):
 class QuestionOption(models.Model):
     question = models.ForeignKey('Question', related_name='options')
     answer = I18nCharField(verbose_name=_('Answer'))
+    position = models.IntegerField(default=0)
 
     def __str__(self):
         return str(self.answer)
 
+    class Meta:
+        verbose_name = _("Question option")
+        verbose_name_plural = _("Question options")
+        ordering = ('position', 'id')
+
 
 class Quota(LoggedModel):
     """
@@ -799,7 +806,7 @@ class Quota(LoggedModel):
 
     Please read the documentation section on quotas carefully before doing
     anything with quotas. This might confuse you otherwise.
-    http://docs.pretix.eu/en/latest/development/concepts.html#restriction-by-number
+    https://docs.pretix.eu/en/latest/development/concepts.html#quotas
 
     The AVAILABILITY_* constants represent various states of a quota allowing
     its items/variations to be up for sale.