Add "do not print if zero" option to spin and doublespin items

[jeromecc]

If the int or double value is equal 0, do not print the item.

[jeromecc]

Instead of using 0 which can be an informative value, we will use "special-value text" to display an empty set symbol when the value is set to minimum.
Minimum will be 0 if the real world value can never be 0, or the nearest (single step) negative value.
For instance, for int, "minimum" could be 0 or -1.
It will be the equivalent of "unset" or "no answer" and the (double) spinbox will not be printed.