added option to remove old events in the settings (issue #2248)

[MariemMARZOUGUI]

Solution for the issue #2248 : in the settings, it is now possible to remove all tasks and events before a specific date by selecting it.

[inson1]

@MariemMARZOUGUI thanks, but SMT are dead. There is already fork https://github.com/FossifyX.