Ability to get data back as a graph
Merge pull request #468 from Oceanleap/pavitra/topic/get_historical_graph
sampling size to be week implemented on graph
Merge pull request #469 from Oceanleap/pavitra/topic/get_historical_graph_by_week
API to get common groups between users, or get all groups for a single user
Merge pull request #470 from Oceanleap/pavitra/topic/Get_Common_groups_for_users
last_sync_time to return -1 for devices that have never posted data