Adjustment sliders: use arrows to live-adjust

In the Adjustment sliders, if you click the text box next to the slider, you can use the up/down arrow keys to change the value, but it doesn’t apply until after you move off that slider. It would be better if it applied “live” as you’re adjust it, and the slider should adjust at the same time.

LrC lets you hover your mouse over the slider and use the arrow keys in the same way, which we should also do.

Originally suggested by Glenn A.