Implement POST for receiving items

- Create new StockItem in the correct location

InvenTree/stock/migrations/0006_stockitem_purchase_order.py

@@ -0,0 +1,20 @@
+# Generated by Django 2.2.2 on 2019-06-15 09:06
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('order', '0010_purchaseorderlineitem_notes'),
+        ('stock', '0005_auto_20190602_1944'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='stockitem',
+            name='purchase_order',
+            field=models.ForeignKey(blank=True, help_text='Purchase order for this stock item', null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='stock_items', to='order.PurchaseOrder'),
+        ),
+    ]