Create "SalesOrderAllocation" object

- Links multiple StockItem objects to a single SalesOrderLineItem

InvenTree/stock/migrations/0031_auto_20200422_0209.py

@@ -0,0 +1,24 @@
+# Generated by Django 3.0.5 on 2020-04-22 02:09
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('order', '0024_salesorderallocation'),
+        ('stock', '0030_auto_20200422_0015'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='stockitem',
+            name='sales_order_line',
+        ),
+        migrations.AddField(
+            model_name='stockitem',
+            name='sales_order',
+            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='stock_items', to='order.SalesOrder'),
+        ),
+    ]