[Icon view] Always open KCMs on single-click
Now that we're clarified that the double-click setting is only supposed to apply to file and folder views, we can make System Settings' icon grid always activate KCMs on single-click (which is what people seem to expect even when using the systemwide double-click setting) because it's not a file or folder view.
BUG: 377309 FIXED-IN: 5.21
cc @teams/vdg