User notifications

PR: https://bitbucket.org/athento/athentose3/pull-requests/1048

The user will be able to see notifications from the product about actions taken.

The notification system will be updated periodically to indicate to the user if any notifications are available.

Notifications are only available for background tasks, that is, when the user has the result of a background task available, a notification is created. Depending on the type of notification, the user will be able to perform the relevant action (in the case of background tasks, he/she will be able to see the results).

The user will be able to delete the notification to view other notifications.