Allow a sub gifter to give subs "on behalf of" another user.

Inevitably, during a hype train or just as part of the regular course of a stream, someone who is normally an avid gifter or just a steady, regular viewer and active chat participant, will express regret that their current financial status doesn't let them gift subs or send bits.

It would be nice to be able for someone (anonymous or not) to gift subs "on behalf of @UserX". Just another way of sharing some of the love around. I think several of the streamers I follow and sub to would welcome such a thing, and I know members of their chats would!