Allow blank PO description and add URL field

InvenTree/order/migrations/0002_auto_20190604_2224.py

@@ -0,0 +1,29 @@
+# Generated by Django 2.2 on 2019-06-04 12:24
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('order', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='purchaseorder',
+            name='URL',
+            field=models.URLField(blank=True, help_text='Link to external page'),
+        ),
+        migrations.AlterField(
+            model_name='purchaseorder',
+            name='description',
+            field=models.CharField(blank=True, help_text='Order description', max_length=250),
+        ),
+        migrations.AlterField(
+            model_name='purchaseorder',
+            name='supplier',
+            field=models.ForeignKey(help_text='Company', limit_choices_to={'is_supplier': True}, on_delete=django.db.models.deletion.CASCADE, related_name='Orders', to='company.Company'),
+        ),
+    ]