support for multilevel kcms
Summary:
Make the title a toolbutton, and when there are multiple levels, make
a breadcrumb out of buttons.
clicking on buttons will navigate the levels(keyboard shortcuts work too)
a similar modification will be needed to be done to KCMShell
depends from D14580
Test Plan:
Added a level to a kcm, works as intended
This latest version works correctly on both the sidebar and icongrid systemsettings mode
Reviewers: Plasma, VDG, davidedmundson
Reviewed By: Plasma, davidedmundson
Subscribers: davidedmundson, abetts, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D14581