Show the presence of highlighted tab outside of the screen
When you join a lot of MUC, there is no way to tell when you are HL on
the 142th one of them if you only have 100 line terminal. :'(
(Especially when you are HL in another tab and think the \a came from
there.)
Maybe highlight a line at the bottom of the tab list meaning "activity
bellow" similar to what tmux does.