[Kicker and Kickoff] Use an icon for the "Edit Applications..." menu entry

Summary:
This adds an icon to the "Edit Applications..." menu entry to make it look better.

Test Plan: Open the right click context menu for Kicker or Kickoff

Reviewers: Plasma, VDG, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: VDG, plasma-devel, Plasma

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D17963