Add missing customer and voucher migrations.

On a fresh install from current master these migrations are missing.
The voucher migration removes the blank parameter from orderlinevouchers.vouchers.
The customer migration changes the editable parameter to False.

ecommerce/extensions/customer/migrations/0002_auto_20160517_0930.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import oscar.models.fields.autoslugfield
+import django.core.validators
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('customer', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='communicationeventtype',
+            name='code',
+            field=oscar.models.fields.autoslugfield.AutoSlugField(populate_from=b'name', validators=[django.core.validators.RegexValidator(regex=b'^[a-zA-Z_][0-9a-zA-Z_]*$', message="Code can only contain the letters a-z, A-Z, digits, and underscores, and can't start with a digit.")], editable=False, max_length=128, separator='_', blank=True, help_text='Code used for looking up this event programmatically', unique=True, verbose_name='Code'),
+        ),
+    ]

ecommerce/extensions/voucher/migrations/0004_auto_20160517_0930.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('voucher', '0003_orderlinevouchers'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='orderlinevouchers',
+            name='vouchers',
+            field=models.ManyToManyField(related_name='order_line_vouchers', to='voucher.Voucher'),
+        ),
+    ]