Prevents requirejs error with perseus exercises loaded.
Fixes #2529
Fixes khan contentload bug. Adds paths to denormed exercise and videos.
Fixes soundmanager to no longer use require js.
Allow content viewing without being logged in.
DRYs up content rendering with no content log available.
Further restricts lockdown. Reduce homepage to link to 'learn'.
Merge pull request #2534 from rtibbles/login_issues

Content rendering fixes