The LMS should serve favicon.ico also when a theme is enabled.
Lower logging level in grading condition from exception to info

addresses part of LMS-2907
Merge pull request #4192 from edx/adam/change-logging-level-gradding

Lower logging level in grading condition from exception to info
Merge pull request #3769 from shindere/favicon-fixup

Improves the way LMS serves /favicon.ico
Move video descriptor instantiation in tests to single place.