Better channel burst system

[SadieCat]

Currently when a user joins a channel they get a names list. This is pretty sparse and doesn't contain a lot of the useful data that a client needs so they need to wait for the JOIN and then send a WHO to retrieve additional data. This is non-ideal and increases delay for rendering the UI. We can do better.

I'm proposing we add a draft/rich-channel-burst cap which changes this to send something more useful for clients. This should probably include a WHOX response line for each user and maybe other things too (e.g. if a user has away-notify then away messages).