Add "install_into" field for BuildItem

- Points to which output stock item it will be going into

InvenTree/build/migrations/0021_auto_20201020_0908.py

@@ -0,0 +1,25 @@
+# Generated by Django 3.0.7 on 2020-10-20 09:08
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0052_stockitem_is_building'),
+        ('build', '0020_auto_20201019_1325'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='builditem',
+            name='install_into',
+            field=models.ForeignKey(blank=True, help_text='Destination stock item', limit_choices_to={'is_building': True}, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='items_to_install', to='stock.StockItem'),
+        ),
+        migrations.AlterField(
+            model_name='builditem',
+            name='stock_item',
+            field=models.ForeignKey(help_text='Source stock item', limit_choices_to={'belongs_to': None, 'build_order': None, 'sales_order': None}, on_delete=django.db.models.deletion.CASCADE, related_name='allocations', to='stock.StockItem'),
+        ),
+    ]