save changeset pk in session instead of session id in changeset

src/c3nav/editor/migrations/0012_remove_changeset_session_id.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.2 on 2017-07-04 20:11
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('editor', '0011_auto_20170704_1640'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='changeset',
+            name='session_id',
+        ),
+    ]