Fix #202 -- Allow the manual ordering of questions

* Allow the manual ordering of questions
Update Unit Tests
Fix some typos

* Add migrations

* Minor notation change

src/pretix/base/migrations/0032_question_position.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.9 on 2016-08-21 19:27
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0031_auto_20160816_0648'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='question',
+            name='position',
+            field=models.IntegerField(default=0),
+        ),
+    ]

src/pretix/base/migrations/0033_auto_20160821_2222.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.9 on 2016-08-21 22:22
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0032_question_position'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='question',
+            options={'ordering': ('position', 'id'), 'verbose_name': 'Question', 'verbose_name_plural': 'Questions'},
+        ),
+    ]

src/pretix/base/models/items.py

@@ -386,10 +386,14 @@ class Question(LoggedModel):
         blank=True,
         help_text=_('This question will be asked to buyers of the selected products')
     )
+    position = models.IntegerField(
+        default=0
+    )
 
     class Meta:
         verbose_name = _("Question")
         verbose_name_plural = _("Questions")
+        ordering = ('position', 'id')
 
     def __str__(self):
         return str(self.question)
@@ -404,6 +408,13 @@ class Question(LoggedModel):
         if self.event:
             self.event.get_cache().clear()
 
+    @property
+    def sortkey(self):
+        return self.position, self.id
+
+    def __lt__(self, other) -> bool:
+        return self.sortkey < other.sortkey
+
 
 class QuestionOption(models.Model):
     question = models.ForeignKey('Question', related_name='options')