[Util] XWrapper::Clear().
[Util] XWrapper::ClearStrut() utility method.
[Util] Better area check.
[Util] XWrapper::GetAvailableGeometry().

Directly iterate over all windows and check their struts instead of relying
on _NET_WORKAREA as QDeskopWidget::availableGeometry() does.

Probably related to https://bugreports.qt-project.org/browse/QTBUG-18380
[SB2] Properly respect other panels in desktop mode.