Counterpart to SPACE, ENTER for changing numerical options

[yinghao-w]

When changing numerical options, ENTER and SPACE both increment the number, but AFAIK there isn't a counterpart key to decrement. BACKSPACE and DEL do not work.

Suggestion: make BACKSPACE decrement.

[BenBE]

+ and - are one option, F7 (Dec) and F8 (Inc) are another. The latter is also documented down in the function bar.

[yinghao-w]

@BenBE yes I'm aware, so not a totally necessary feature, but just something that could be nice to have (of course if it fits with the general UI style).