Marking item completion not prevented when context is frozen

This needs to be tested in both the web interface and with the mobile app. Create a course with some students. Enable course completion and add a label. Enable the context freezing feature. Ensure that the student can mark the activity as complete, and then mark it as incomplete. Ensure that an unenrolled administrator can mark the activity as complete, and then mark it as incomplete. Repeat steps 1-2 in the mobile app. Freeze the course. Ensure that the student cannot mark the activity as complete. Ensure that the administrator cannot mark the activity as complete. Repeat steps 5-6 in the mobile app.