Summary:
Moves the LnF KCM from the Workspace Theme category to the top level (to the Appearance section), because:
- the KCM affects everything, not just workspace themes
- then it's faster to discover the KCM and go to it
It won't affect any other KCMs, so this change should be fine.
Also see T8871.
{F6604946}

Test Plan: Open the system settings.

Reviewers: #plasma, #vdg, rooty, ngraham, davidedmundson

Reviewed By: #plasma, #vdg, rooty, ngraham, davidedmundson

Subscribers: ngraham, davidedmundson, abetts, rooty, #vdg, plasma-devel, #plasma

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D18892