Added new error message that displays when HTML5 video is not supported altogether. Make sure spinner gets hidden when error message is shown. [BLD-638]
Merge pull request #3631 from edx/jmclaus/bugfix_display_specific_error_message_when_HTML5_video_not_supported

Added new error message that displays when HTML5 video is not supported. [BLD-638]
Tolerance expressed in percentage now computes correctly. [BLD-522]
Modified and extended tests on percentage expressed tolerance.
Addressed comments.
All tests pass now.
Added tests for compare_with_tolerance
Put unit tests of util in their own file.