As a user I want to be notified about selected tasks

[robin92]

A user wants to manually select tasks (deadline required) and set a custom notification for each. For instance, having the following tasks

id    due    description          urgency
1     6h     clean the house      10
2     3d     pay the energy bill  8
3            update system        2

a user may set a notification 1 hour before due date for 1 and notification 15 minutes prior to task 2. Setting a notification for 3 is not possible as this task hasn't got a due date.