Option to hide join/part/quit messages from the chat window based on recent user activity

[gdamjan]

I don't need to see parts and joins in the chat pane.

konversation handles this nicely, it only shows parts for people that were recently active (last 5 minutes).

[Venemo]

@gdamjan Right now we group together multiple join / part / quit messages, so that should reduce the noise. If I understand correctly you don't actually want to hide all of them, just want to show them based on user activity. Do I understand correctly?

[gdamjan]

@Venemo right, if a user was recently active I'm concerned about them leaving the chat,
if not, I don't care at all.

[Venemo]

This should be solved together with #95