Refactor

As all points from the epic refactor issue are closed #47 (closed) I am merging this in to master in order to unblock development.

backend/core/migrations/0003_student_matrikel_no.py

+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.7 on 2017-11-10 21:46
+from __future__ import unicode_literals
+
+import core.models
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0002_auto_20171110_1612'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='student',
+            name='matrikel_no',
+            field=models.CharField(default=core.models.random_matrikel_no, max_length=8, unique=True),
+        ),
+    ]