[emacs] experiment with EXWM and key bindings

- Binding C-w to cut isn't worth the effort. I close tabs way more
  often.
- When launched from within Emacs, Rofi doesn't seem to be able to
  properly launch programs. I haven't been able to debug the issue.
- Rofi seems to have a noticeable lag now under EXWM, compared to back
  when I was using bspwm. rofi-pass is the main reason I still use
  it. So,
        TODO: see if I can port rofi-pass to ivy or helm.
- EXWM's `exwm-input-set-key' seems awfully verbose compared to sxhkd.
  See if there's a shorter and neater way.