Add PurchaseOrderAttachment model

- File attachment against PurchaseOrder

InvenTree/order/migrations/0016_purchaseorderattachment.py

@@ -0,0 +1,27 @@
+# Generated by Django 2.2.9 on 2020-03-22 07:01
+
+import InvenTree.models
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('order', '0015_auto_20200201_2346'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='PurchaseOrderAttachment',
+            fields=[
+                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('attachment', models.FileField(help_text='Select file to attach', upload_to=InvenTree.models.rename_attachment)),
+                ('comment', models.CharField(help_text='File comment', max_length=100)),
+                ('order', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='attachments', to='order.PurchaseOrder')),
+            ],
+            options={
+                'abstract': False,
+            },
+        ),
+    ]