This adds a fallback routine where the tray window will
get notified whenever the bar window changes its visibility
state. Required in case of failure to restack the tray container
above the bar window in the window stack.
Fixesjaagr/lemonbuddy#95
If the tray is being activated while clients are in
the process of getting dismissed by another MANAGER
they will not receive the new MANAGER broadcast.
Delayed broadcasts are sent to make sure they're notified.