[Icon Applet] Don't copy application .desktop files to plasma_icons if...

[Icon Applet] Don't copy application .desktop files to plasma_icons if run_desktop_files restriction is enforced

When this restriction is enabled, KIO will refuse to run desktop files outside system-known locations
essentially breaking the icon widgetin this case. Since we still want to be able to have shortcuts
in locked-down setups, let's just use the source desktop file in this case and rather lose the ability
to customize it (which isn't really possible with this restrition anyway)