FR: Open error message when clicking on an error notification.

[real-yfprojects]

The problem

Reported in #1773
When a scheduled backup fails the user is notified (when enabled) that there was an error. However he has no easy way to quickly look at the error message.

Requested Solution

Clicking on the notification should open a window where the user can easily read the error message.
(Before implementing this it would be good to improve the way vorta handles borg errors and displays them to the user)

Additional context

#1522 is a prerequisite for this.