Add immutability to KCM Icons
Summary: Add immutability to KCM Icons, disable theme delegate and not the whole grid in order to allow user to change icon size if not immutable too
Test Plan: Add [$i] to kdeglobals key
Reviewers: Plasma, ervin, ngraham, crossi, meven
Subscribers: broulik, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D26045