added created field to users api
position of user in completions and course avg

added completions to response dict

Merged course completions leaders and course avg

added is_active check

pep8 compliant

remove serialiser class
ooyala: update hash
Merge pull request #113 from edx-solutions/ziafazal/course-completion-leaders

course completions leaderboard
adding proficiency metrics

added active filter

added tests
Merge pull request #116 from edx-solutions/ziafazal/course-proficiency-position

adding proficiency metrics
Merge pull request #112 from edx-solutions/ziafazal/add-created-field-to-user-serializer

added created field to users api
mattdrayer/api-currentcontentid: GET response now returns content position_tree