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

Change icon resolution to separate if clauses. This allows each fallback
method to attempt icon loading regardless of whether previous parameters
were provided but failed to resolve.

For example, previously if an application provided an empty or invalid
icon parameter, the daemon would skip all other checks and no icon would
be resolved, even if the other checks would have succeeded in resolving
an icon.

When a notification provides an app_name but no explicit icon, attempt
to derive the application icon from the desktop entry as a fallback
mechanism.

The mate-notification-properties binary had no command-line option
parsing, making it hard to know the installed version.

This adds the version flag to both mate-notification-properties and
mate-notification-daemon.

Fixes #228

Add a new 'force-display' gsettings and checkbox that, when enabled,
shows all notifications regardless of urgency, fullscreen, or
screensaver state.  Do Not Disturb still takes precedence.

Fixes #199

Since we have notifications history now, we can make changes to align
a bit better with the spec.

- Critical notifications should always be shown and should never
  automatically expire. They should only be closed by user action.

- Previously, the only notifications that bypassed fullscreen and
  screensaver suppression were persistent ones. Now, since critical
  notifications are persistent, we downgrade normal notifications to
  only play sound on fullscreen.

- Low urgency notifications do not show nor play sound when on
  fullscreen.

- Do Not Disturb still suppresses all notifications, including critical.

When a notification is removed from the hash table, any pending idle
reposition source must be explicitly canceled in to avoid attempting to
remove an already-removed source.

This prevents the race condition where the timeout fires and
auto-removes itself before the notification cleanup tries to cancel it.

Prevent daemon from exiting when history tracking is enabled to preserve
the in-memory notification history.

Add destroy notify callback to prevent use-after-free crashes when
notifications are closed before their reposition timeout fires.

Fixes #236

Add checks for monitor_id to prevent crash during monitor change events.
Instead it falls back to last available monitor and allows notification
processing to continue without a monitor.

Fixes: #200