Show join & leave messages

[hackergrrl]

Ideally configurable, it would be useful to see in the chat history when people join and leave channels you're in. For cabal-client, this could be events, or virtual messages like the moderation status messages we do.

[cblgh]

was thinking about this earlier in the week: if we ever add this i think the default should be opt-in, as opposed to the opt-out of all other chat softwares i know of :)

it's just so needlessly messy, especially for low-activity channels. people also rarely know they can turn it off