contest and contest_problems api.

add ordering for contest and submission models

submission/migrations/0004_auto_20170717_1324.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.6 on 2017-07-17 13:24
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('submission', '0003_auto_20170704_1243'),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name='submission',
+            options={'ordering': ('-created_time',)},
+        ),
+    ]