Move real_name to UserProfile;

Delete student_id field;
Mark the problems that have submission;
Alter dispatcher to adapt the changes.

utils/captcha/views.py

@@ -2,10 +2,9 @@ from base64 import b64encode
 
 from . import Captcha
 from ..api import APIView
+from ..shortcuts import img2base64
 
 
 class CaptchaAPIView(APIView):
     def get(self, request):
-        img_prefix = "data:image/png;base64,"
-        img = img_prefix + b64encode(Captcha(request).get()).decode("utf-8")
-        return self.success(img)
+        return self.success(img2base64(Captcha(request).get()))