Refactor statusline by clearly separating the rendering part from the
text display. Use printf-like format string for statusline
customization.
Document printf-like format string to customize the statusline.
Allow to completely mute the statusline (except for push notifications)
with a format specifier.
Provide a display mode with unicode icons for the status elements.
Implements: https://todo.sr.ht/~rjarry/aerc/34
Signed-off-by: Koni Marti <koni.marti@gmail.com>
Acked-by: Robin Jarry <robin@jarry.cc>
