Add grouping and "Show Only Minimized" options to icons-only task manager
Being able to disable grouping for the icons-only task manager makes sense, because it has enough space to hold plenty of application icons/launchers. The "Show only tasks that are minimized" option is useful as well for the IOTM.
Test Plan: Open the IOTM behavior settings page. Enable/disable grouping and toggle the "Show only tasks that are minimized" option.
Reviewed By: VDG, ngraham
Differential Revision: https://phabricator.kde.org/D23242