optionally show a history of notifications
Summary:
Bug 378032.
With these changes, notifications can be configured to always persist in the notifications applet.
Todo: filter by application, see https://bugs.kde.org/show_bug.cgi?id=378032#c27
Test Plan: Open the notification plasmoid's settings. Check 'Show a history of notifications'. Trigger some notifications. They should show up in the applet.
Reviewers: Plasma, VDG, davidedmundson
Reviewed By: Plasma, davidedmundson
Subscribers: mart, graesslin, davidedmundson, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D7271