Tests: fix NotificationManager by adding missing functions

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Notifications: tune margins and use notification manager to close notifications

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
CardsPage: fix anchoring for the display of launchers

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>