Indicate pre-selected multi-value item

Issue #32 

Last selected item has a checkmark next to it and when a new item is selected the background goes gray. Once the user goes back to the home tableview of the debug menu the checkmark will update to the new selection and will display accordingly the next time they open the multi-value item tableview
Actually, you shouldn't need to change the background view's color for selected. Just use highlighted to do that, depending on whether `highlighted` is true or not. The system will set highlighted to `false` as soon as you lift up on the cell touch.