Feature Request: New Method to Bulk Add Users to a Group

[RiteshTC]

Topgear requirement:
Add 10 default user admins to every new Topgear group created.
This will be useful in the admin tool as well, as users are mostly added in bulk.

Feature Request:
Create a method to accept an array of user Ids to be bulk added to a group at once.
Feature can be restricted to admin user or M2M token only