Add 'allocated' status code to build

- This means that parts have been taken from stock

InvenTree/build/migrations/0011_auto_20190508_0748.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.2 on 2019-05-07 21:48
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('build', '0010_auto_20190505_2233'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='build',
+            name='status',
+            field=models.PositiveIntegerField(choices=[(10, 'Pending'), (20, 'Allocated'), (30, 'Cancelled'), (40, 'Complete')], default=10, validators=[django.core.validators.MinValueValidator(0)]),
+        ),
+    ]