Introduce original price (#905)

* Introduce original price

* Rebase and styling

* Widget

src/pretix/base/migrations/0092_auto_20180511_1224.py

@@ -0,0 +1,23 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.11 on 2018-05-11 12:24
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ('pretixbase', '0091_auto_20180513_1641'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='item',
+            name='original_price',
+            field=models.DecimalField(blank=True, decimal_places=2,
+                                      help_text='If set, this will be displayed next to the current price to show '
+                                                'that the current price is a discounted one. This is just a cosmetic '
+                                                'setting and will not actually impact pricing.',
+                                      max_digits=7, null=True, verbose_name='Original price'),
+        ),
+    ]