Improve automatically adding and showing channels on join or activity

This appears to be aggressively unhiding all chats with any activity, even if temporarily hidden again. I may be mistaken, but I don't think the desktop client unhides Temporarily Hidden buffers on any activity, just messages/notices/etc. Or it might just be unhiding too much on (re)connect given some buffers don't appear to have any new activity. (*I'm out on a trip at the moment, not able to debug right now; I'll have to investigate this more when able.*)