Fix errors when running runserver in python 3.

- The fields need to be unicode not bytes.  In python 2 it was auto
converting.
- The static url base has been allowed to be a unicode string for a
while.

common/djangoapps/student/migrations/0022_indexing_in_courseenrollment.py

@@ -14,6 +14,6 @@ class Migration(migrations.Migration):
     operations = [
         migrations.AddIndex(
             model_name='courseenrollment',
-            index=models.Index(fields=[b'user', b'-created'], name='student_cou_user_id_b19dcd_idx'),
+            index=models.Index(fields=['user', '-created'], name='student_cou_user_id_b19dcd_idx'),
         ),
     ]