Disable range requests in pdf.js (Not to be merged)

https://openedx.atlassian.net/browse/TNL-488

The first commit causes the pdfviewer to be loaded from courses.edx.org instead of from the current host. To test
1. Import a course into devstack while keeping the same id as on courses.edx.org.
2. Checkout first commit.
3. Try to replicate the issue.

To test the fix:
1. Checkout 2nd commit.
2. In Chrome goto Settings > Show advanced settings > Clear browsing data and delete 'Cached images and files' from the last month.
3. Try to replicate the issue.