Fix IDEUI-293 Improve notification behaviour

Introduce slight modifications in notification pop-up behaviour:
* If the notification is not important, it is shown and then hide
automaitically after 5 secs (hard-coded delay),
* If the user closes the notification, it hides it,
* If the user overs the notification, automatic hiding is suspended and
spawned again when the mouse leave the notification,
* On one of this status change: message, type, status, state, the
notification is updated accordingly but the pop-up is not reshown,
* On important status change, the notification is reshown whereas it has
been closed by the user or automatically hidden, it then follows the
rules associated to important notifications (always on pop-up),
* When getting in FINISHED status, whereas important or not the
notification is automatically hidden.
Merge pull request #203 from stephanedaviet/IDEUI-293

Fix IDEUI-293 Improve notification behaviour