Since libi3 currently creates its own cairo surface for drawing text, we
need to mark our own surface as dirty to force cairo to invalidate its
cache. Otherwise, this will result in graphical glitches such as the text
not showing up at all.
This wrapper can be removed in the future when libi3 is adapted to reuse
the same cairo surface as we do for all other drawing operations.
This patch creates all necessary windows for i3bar with 32-bit visuals if available.
It also introduces the possibility to define RGBA colors (next to RGB colors), which
allows the user to set the opacity of any color. This requires running a compositor.
With this patch we also start supporting _NET_SYSTEM_TRAY_VISUAL, which is necessary
for the tray icons so they create the tray window with the correct depth and visual.
