VisibleBlocks migration: add course_id for bulk retrieval

lms/djangoapps/grades/migrations/0004_visibleblocks_course_id.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+from opaque_keys.edx.keys import CourseKey
+import xmodule_django.models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('grades', '0003_coursepersistentgradesflag_persistentgradesenabledflag'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='visibleblocks',
+            name='course_id',
+            field=xmodule_django.models.CourseKeyField(default=CourseKey.from_string('edX/BerylMonkeys/TNL-5458'), max_length=255, db_index=True),
+            preserve_default=False,
+        ),
+    ]