Add a List function that understates unselected items

[abdulshaikh55]

Problem

When I implement highlight_symbol() for a List this is what it looks like:

    Eat
    Sleep
[*] Code
    Repeat

I want it to be something like this:

[ ] Eat
[ ] Sleep
[*] Code
[ ] Repeat

Solution

I have tried to do it and this is my first time. But I must be doing something wrong. It is fairly easy. Instead of blank_symbol, if understate_symbol() is selected, use that symbol.

Alternatives

A function that asks for both; the highlight symbol as well as the understate symbol.

Potential names of the function: (they are all antonyms for highlight)
understate_function
discount_function
lowlight_function

Additional context

[joshka]

I like this idea - I'm not sure that the names make sense to me though. Probably unselected_symbol or something similar would be fine (and I wonder whether we should consider whether highlight symbol is worth renaming?)