Add (optional) URL to stock tracking info

InvenTree/stock/migrations/0008_stockitemtracking_url.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.2.2 on 2019-07-15 11:10
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('stock', '0007_auto_20190618_0042'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='stockitemtracking',
+            name='URL',
+            field=models.URLField(blank=True, help_text='Link to external page for further information'),
+        ),
+    ]