Bug fix for ensuring location and category names are unique for common parent (#4361)

* Update Meta class for StockLocation and PartCategory

* Migration files

* Add extra unique requirements to  InvenTreeTree model

- unique_together does not work as expected with null values

InvenTree/stock/migrations/0093_auto_20230217_2140.py

@@ -0,0 +1,17 @@
+# Generated by Django 3.2.16 on 2023-02-17 21:40
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0092_alter_stockitem_updated'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='stocklocation',
+            options={'verbose_name': 'Stock Location', 'verbose_name_plural': 'Stock Locations'},
+        ),
+    ]