Receive selected activites only

[bassner]

It'd be nice to be able to select only specific to activity types that we want to receive in PRESENCE_UPDATE events, and ignore other updates.

I was looking for a way to find all members that are currently streaming on Twitch without receiving the whole mass of activity updates on large servers. I'd like to avoid the big amount of traffic that is usually coming with enabling presence updates, but I am still interested in activities of type 1, and would like to drop other types (except for one empty activities array to clear the state after streaming ended, maybe).

That would enable features like a streamer overview on a server without causing too much traffic on both Discord's infrastructure and the bot. :)