contest and contest_problems api.

add ordering for contest and submission models

contest/urls/oj.py

@@ -1,9 +1,9 @@
 from django.conf.urls import url
 
-from ..views.oj import ContestAnnouncementListAPI, ContestListAPI
+from ..views.oj import ContestAnnouncementListAPI, ContestAPI
 
 urlpatterns = [
-    url(r"^contest/?$", ContestListAPI.as_view(), name="contest_api"),
+    url(r"^contest/?$", ContestAPI.as_view(), name="contest_api"),
     url(r"^contest/announcement/?$", ContestAnnouncementListAPI.as_view(), name="contest_announcement_api"),
 
 ]