When clicking the close button on a notification, the D-Bus signal
incorrectly sent reason=1 (expired) instead of reason=2 (dismissed).

Fixed by setting a flag on the notification window in the close button
callback before destroying it, and checking this flag in the callback to
send the correct close reason.

Fixes #129

When compositing is disabled, notifications have a rounded shape mask
applied but it's not redrawn. This change queues a redraw after applying
the shape region so the notification shows rounded corners.

Fixes #98

Countdown was only visible for notifications that had action buttons.
This change adds a 'show-countdown' gsetting to display it instead on
all non-persisntent notifications.

Allow to set coutdown color from .countdown:selected for all themes
Fix the countdown for slider theme and draw transparent background for countdown