Expose "is_allocated" parameter on StockItem API

InvenTree/stock/migrations/0029_auto_20200421_2359.py

@@ -0,0 +1,19 @@
+# Generated by Django 3.0.5 on 2020-04-21 23:59
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0028_auto_20200421_0724'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='stockitem',
+            name='status',
+            field=models.PositiveIntegerField(choices=[(10, 'OK'), (50, 'Attention needed'), (55, 'Damaged'), (60, 'Destroyed'), (70, 'Lost'), (110, 'Shipped'), (85, 'Returned')], default=10, validators=[django.core.validators.MinValueValidator(0)]),
+        ),
+    ]