Keep AppletMenu as small as possible
Summary:
In retrospect there's no need to fill the width, if people want that
effect they can add a spacer; whereas you can't do the opposite.
Also set the size to 0 when it's empty. This mean using status as
normally PanelContainment ensures plasmoid's are a minimum of a square.
BUG: 374996
Reviewers: Plasma
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D4115