Move groups models from users app, add groups index, add stubs for create groups
Merge branch 'develop' into group_management

fix registration bug
Add view and validation for create group
Add delete group feature
Add group edit view and delete user from group
Merge branch 'develop' into group_management
Add user adding to group, modify user search API for including avatars and fullnames
Merge branch 'group_management' into develop

Issue #2