Fix sorting of items

W.T.F past self. Char field for a reference number?!

training/migrations/0010_auto_20211228_1144.py

@@ -0,0 +1,23 @@
+# Generated by Django 3.1.13 on 2021-12-28 11:44
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('training', '0009_auto_20211221_1539'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='trainingcategory',
+            name='reference_number',
+            field=models.IntegerField(unique=True),
+        ),
+        migrations.AlterField(
+            model_name='trainingitem',
+            name='reference_number',
+            field=models.IntegerField(),
+        ),
+    ]