添加contest权限验证、contest密码验证api

添加problem、contest单元测试。

contest/urls/oj.py

@@ -1,9 +1,11 @@
 from django.conf.urls import url
 
 from ..views.oj import ContestAnnouncementListAPI, ContestAPI
+from ..views.oj import ContestPasswordVerifyAPI
 
 urlpatterns = [
     url(r"^contest/?$", ContestAPI.as_view(), name="contest_api"),
+    url(r"^contest/password/?$", ContestPasswordVerifyAPI.as_view(), name="contest_password_api"),
     url(r"^contest/announcement/?$", ContestAnnouncementListAPI.as_view(), name="contest_announcement_api"),
 
 ]