Option to add/remove multiple users from a group with just one call and one response

[dragos-boisteanu]

Describe the solution you'd like

For the { set }client to server message a new field should be added called subs, this field should be an array of objects like:
[ { user: "id", mode: "modeValue"}, { user: "id", mode: "modeValue"}, { user: "id", mode: "modeValue"},...]

For the { del } message a new field called users that is an array of objects like:
users: ["id", "id", "id"] instead of user: ""

The sub and user fields should be kept so it won't brake existing clients.

Thank you.