Added support for rolling an X sided die

Per issue #3, I added support for rolling a die of any number greater than 0. I based the number input off of the same one used in the WishList and Trade Cards fragments to keep the style similar.

I attempted to use the built in Android NumberPicker but it's not fully available and leaves out important features like the up and down options. We could extend that if we wanted an actual number picker, but there are libraries that seem to have better NumberPickers if we wanted a better looking picker.