Oleg/lti graded additional tests

- Includes new and updated Python tests for the LTI module.
- Includes fix for <b>BLD-465</b>: e-reader error when popping out window.

<b>Description of BLD-465</b>
The attached error is seen when attempting to pop out the e-reader in a different window - happens about 50% of the time. Can be seen in 2.03x here: https://courses.edx.org/courses/MITx/2.03x/3T2013/courseware/Course_Text/Textbook/# . Also noted in 4.605x course.

<b>Note</b>
Because originally the branch of this PR was branched off from <b>rc/2013-11-21</b> branch, this PR must wait before <b>rc/2013-11-21</b> gets merged into <b>master</b>.

Work in progress, do not merge!