KCM/GlobalShortut: convert FOREACH and old signal syntax

Test Plan: Builds, changed a shortcut and back again

Reviewers: ervin, bport, crossi, hchain, #plasma

Reviewed By: ervin

Subscribers: ahmadsamir, davidedmundson, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28282