Move SupplierPart and SupplierPriceBreak to the 'Company' app

- https://docs.djangoproject.com/en/2.2/ref/models/options/#django.db.models.Options.db_table
- https://stackoverflow.com/questions/3519143/django-how-to-specify-a-database-for-a-model
- And others, presumably

InvenTree/stock/migrations/0017_auto_20190518_1759.py

@@ -0,0 +1,19 @@
+# Generated by Django 2.2 on 2019-05-18 07:59
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0016_auto_20190512_2119'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='stockitem',
+            name='supplier_part',
+            field=models.ForeignKey(blank=True, help_text='Select a matching supplier part for this stock item', null=True, on_delete=django.db.models.deletion.SET_NULL, to='company.SupplierPart'),
+        ),
+    ]