This (partially) reverts commit 127bbdf653.
Only incorrect changes from Kirigami.Units.largeSpacing to
Kirigami.Units.gridUnit are reverted. Only Plasma.Units were buggy.
We need to specify the width manually when porting to ItemDelegate. Also
we can port to CheckDelegate instead here since it does exactly the same
thing as the old list item's custom content item.
CCMAIL: notmart@gmail.com