Display an image response in the course staff debug page
Implement leaderboard feature
Merge pull request #586 from edx/will/leaderboard-squashed

Implement leaderboard feature
Add Andrew Dekker to the AUTHORS file
Small developer doc formatting fixup
Merge pull request #584 from edx/will/image-staff-debug

Display an image response in the course staff debug page
Merge pull request #587 from edx/will/small-doc-fixup

Small developer doc formatting fixup
Update i18n messages
Merge pull request #588 from edx/will/i18n-syncup

Update i18n messages
Update lxml to 3.3.5