[Kicker] Rename id column to itemColumn

In Qt 5.12 new magic `column` and `row` properties appeared in the delegate's scope, similar to the `index` and `model` (`modelData`) one.
This causes `column` to access that (being always the number zero for this list model) and as such the delegate not having a width and turning invisible.

Differential Revision: https://phabricator.kde.org/D16316

applets/kicker/package/contents/ui/ItemMultiGridView.qml

@@ -83,7 +83,7 @@ PlasmaExtras.ScrollArea {
     }
 
     Column {
-        id: column
+        id: itemColumn
 
         width: itemMultiGrid.width - units.gridUnit
 
@@ -91,7 +91,7 @@ PlasmaExtras.ScrollArea {
             id: repeater
 
             delegate: Item {
-                width: column.width
+                width: itemColumn.width - units.gridUnit
                 height: headerHeight + gridView.height + (index == repeater.count - 1 ? 0 : footerHeight)
 
                 property int headerHeight: (gridViewLabel.height