new api to get list of workgroups by group
Updated Group Project XBlock Hash
Merge pull request #111 from edx-solutions/ziafazal/get-workgroups-of-a-group

new api to get list of workgroups by group - LGTM :+1: merging to allow group project XBlock to access it
Group Poejct XBlock update to use new API endpoint
position of user in completions and course avg

added completions to response dict
Merged course completions leaders and course avg