Several changes to models

Add __str__ methods with unicode compatibility.

Make trainer fields optional as they should be.
Include these migrations and apply to DB.

Install some test data in the DB.

training/migrations/0002_required_fields.py

@@ -0,0 +1,30 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+from django.conf import settings
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('training', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='trainingrecord',
+            name='assessed_trainer',
+            field=models.ForeignKey(related_name='trainingrecords_assessed', blank=True, to=settings.AUTH_USER_MODEL, null=True),
+        ),
+        migrations.AlterField(
+            model_name='trainingrecord',
+            name='completed_trainer',
+            field=models.ForeignKey(related_name='trainingrecords_completed', blank=True, to=settings.AUTH_USER_MODEL, null=True),
+        ),
+        migrations.AlterField(
+            model_name='trainingrecord',
+            name='started_trainer',
+            field=models.ForeignKey(related_name='trainingrecords_started', blank=True, to=settings.AUTH_USER_MODEL, null=True),
+        ),
+    ]