Support running in split-screen terminal

[JKrag]

If you are working in an environment where you can open multiple terminals, whether it is a terminal that supports splitting (like iTerm or hyper), tmux, or even just opening multiple windows, then it might be useful to run the actual typing part in one window and live updating message output in another, to get a more Slack like feeling. This could potentially be extended with a third window listing existing channels, and ideally showing which ones have new messages.

In this use case, I envision running the interactive chat in one session, and running a live refreshing output in the other, to actually give you live chat. To do this, it would need a run-mode that just does the live refresh without waiting for any user input, and a modification of the existing run-mode where it doesn't have to print out incoming messages.