Resolve "2FA"

Closes #91 (closed) TODO:

• https://django-two-factor-auth.readthedocs.io/en/stable/installation.html#yubikey-setup
• Add custom settings for two_factor (Gateways, max digits for codes,…)
• Rebuild templates
• Add two_factor settings to account menu

biscuit/core/migrations/0004_otp_yubikey.py

+from django.db import migrations
+
+from otp_yubikey.models import ValidationService
+
+def create_validation_service(apps, schema_editor):
+    ValidationService.objects.create(
+        name='default', use_ssl=True
+    )
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0003_school_logo.py'),
+    ]
+
+    operations = [
+        migrations.RunPython(create_validation_service),
+    ]