Add support for logging in to multiple discord accounts

[BatteredBunny]

Would be nice if you could login to multiple discord accounts

[xangelix]

still needed for actually replacing Discord puppet bridge in my use case! otherwise I think there's feature parity (and much more)

[euanong]

@xangelix if you're desperate for this feature, it's possible to host multiple instances of the bridge :)

(it's possible, but slightly annoying / painful)

[tezlm]

Another +1 here: so many communities/projects have their own guilds to the point that I've hit the 100 guild cap. I'd rather be able to use more accounts than need to leave some or buy nitro.