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.

The notification had a top margin of 8px but no corresponding bottom
marging, making notifications look unbalanced. Added matching bottom
margin.

Also increased the image padding to make it horizontally symetrical and
removed several unused defines.

Fixes #116

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

Style notification history rows based on urgency. Critical notifications
get a red accent bar, low priority notifications are dimmed.