[api2] add api for listing registered accounts (used by admin only)
[api2] add account creating and deleting apis (used by admin only)
[api2] custom defined HTTP status code does not reside in rest_framework.status module, remove the status namespace
[api2] add serializer for validating fields when creating new account
[api2] change to return object list when listing accounts
[api2] Update accounts api handlers
Merge branch 'swpd-master'