FR: Add marks for 0, 0.5, 1

I did not add any marks because by default they also claim some space, and that would have messed up the spacing hard into an ugly mess of bad

However that was cowardice on my part because that's nothing a bit of CSS cant handle. I just dislike messing with CSS a lot and playing with the Interactive tool annoys me

this could complement well the label marks and make the app feel more complete