Add screen information to the declarative view

- To help QML gui handle multiple screen, the Window
  object now holds some screen related properties:
  screenCount, screenNumber, screenGeometry, primaryScreen
Switch to latest notification on show

- Displaying the widget, e.g. when notifications are
  re-enabled, move to the latest notification
Fix removal of hidden notification

- CloseNotification() was failing to remove hidden notifications
- When notifications are disabled and a notification is closed due to
  timeout CloseNotification() is called, the model will
  not suffer changes but the notification need to be removed
Avoid fake inserts into the model

- When a notification is created using Notify()
  the model was ALWAYS changed through the insertRows
  methods and count notification signal - but when
  notifications are disabled there is no need to call
  these functions for a non critical notification
Add property with hidden notification count

- A new property in the model now holds the number
  of notifications that are hidden (because notifications
  are disabled)
- Throwed in a tray icon to call for attention