fixed migrations to work around transaction limitations of SQLite

src/c3nav/mapdata/migrations/0012_rename_section_to_level.py

@@ -2,6 +2,7 @@
 # Generated by Django 1.11.2 on 2017-06-11 12:06
 from __future__ import unicode_literals
 
+from django.conf import settings
 from django.db import migrations, models
 import django.db.models.deletion
 
@@ -79,3 +80,6 @@ class Migration(migrations.Migration):
                                     to='mapdata.Level', verbose_name='level'),
         ),
     ]
+
+    # workaround as transactions are not supported on SQLite because they would break referential integrity
+    atomic = settings.DATABASES['default']['ENGINE'] != 'django.db.backends.sqlite3'

src/c3nav/mapdata/migrations/0017_point_to_poi.py

@@ -2,6 +2,7 @@
 # Generated by Django 1.11.2 on 2017-07-08 14:23
 from __future__ import unicode_literals
 
+from django.conf import settings
 from django.db import migrations, models
 import django.db.models.deletion
 
@@ -41,3 +42,6 @@ class Migration(migrations.Migration):
                                     to='mapdata.Space', verbose_name='space'),
         ),
     ]
+
+    # workaround as transactions are not supported on SQLite because they would break referential integrity
+    atomic = settings.DATABASES['default']['ENGINE'] != 'django.db.backends.sqlite3'