Added questionmark icons

Updated, working and tested.
For the moment the checkbox onclick logic goes full/half check -> ? -> empty -> ? -> full/half check.
The only exception is when there is no restriction selected in the main list, that is in order to integrate the Are you sure? dialog.

An alternative idea for protecting existing settings is to have onclick toggle asked, and only clear the checkbox if you double click. A single click would show a Toast "Double-click to clear".