Having a global set margins and orientation (that were calculated from the panel containment) caused a lot of issues with the way bindings were evaluated across panels, and with high coupling.
Now use properties from within containments to determine shell margins instead, which removes the dependency on other containments for measurements. This allows us to get rid of TaskPanelControls as well!
Fixes: https://invent.kde.org/teams/plasma-mobile/issues/-/issues/198
Hi, this implements a close all button for the task switcher.
Regarding the double check (`Clear All` -> `Are you sure?`), as far as I know, no system has such a feature for this kind of operation, at the moment, so take it as a proposal.
Move from a C++ library + QML plugin to a QML plugin only for simplicity, since the homescreen switching architecture will be done from Plasma, and so use of the shell library only needs to be from QML.
