#18 More refine validation for GFXIntegerNumber GFXDoubleNumber

[Cinly Ooi]

GFXIntegerNumber and GFXDoubleNumber at present supports min,max value. It might be advisable to extends to to include ranges of values.

For example, an application might requires integer number -1,0,3,4. At present, it will be necessary to write it as [-1,4], meaning the two values that are not needed, 1 and 2 cannot be detected appropriately.

The alternative solution, a drop-down list for all values using GFXSelection is less intuitive.