When increasing the value displayed in a spinbox, normally the least
significant digit should stay in place to avoid unecessary movement.
This means the numbers should be right-aligned, instead of being
left-aligned like they are currently.
Since right-aligning still looks a bit unbalanced, centering should be a
good middle ground. In addition, when the number of digits does not
change it makes more sense to pad the number on both sides equally in