[applets/appmenu] Set iconSource properly
Summary: setting an icon via i18n makes no sense
Test Plan: Put in vertical panel, had an icon
Reviewers: Plasma, broulik, ngraham
Reviewed By: Plasma, broulik, ngraham
Subscribers: ngraham, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D18480