[Task Manager] Don't show redundant "Actions" header in context menu with nothing but actions in it
Previously, the Actions header was always shown, even when the context menu
consisted of nothing but actions. This is unnecessary since a menu's normal state is
to show nothing but actions.
With this patch, the Actions header is only shown for context menus that have
more than one section.
Context menu with only actions:
Context menu with nore than just actions:
Reviewers: broulik, Plasma, hein
Reviewed By: Plasma, hein
Differential Revision: https://phabricator.kde.org/D20846