[Notifications] Disable history check box when notifications are disabled

Authored by broulik on Jan 19 2018, 9:55 AM.

Description

[Notifications] Disable history check box when notifications are disabled

You cannot have a history of notifications if you don't get any notifications in the first place.
Also move checkbox below notification history as it's semantically related.

Differential Revision: https://phabricator.kde.org/D9979

(cherry picked from commit c81a0151f50ef03ecfe8bea2d331af9e74cdb63f)