修改group的models添加小组管理员的多对多字段，把原来的管理员字段重命名为创建者

group/migrations/0006_auto_20151209_1834.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9 on 2015-12-09 10:34
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('group', '0005_joingrouprequest_accepted'),
+    ]
+
+    operations = [
+        migrations.RenameField(
+            model_name='group',
+            old_name='admin',
+            new_name='created_by',
+        ),
+    ]