Replace size options with a scale input

The size option could be more customizable with a scale input.

The size dropdown should be replaced by a number input spinner (input field with up/down arrows).
The spinners input is the percentage of the card size. Default value should be 100 = normal card size.

Minimum value should be at least 1. We don't want to divide by 0 to check how many cards fit on a sheet.
Arrows (if included) should inc/dec by 1 (not below minimum)
Maximum is optional.