expose toggleWidgetExplorer through dbus
Summary:
--shows/hides the WidgetExplorer through dbus
Test Plani: trigger widget explorer from command line
Reviewers: mart, davidedmundson, Plasma
Reviewed By: davidedmundson, Plasma
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D3754