Support commerce price field

I have attached a patch that I believe provides a start for this.

Additionally, this patch contains a proposed change to the js event used to update the value of the slider from the textfield (keyup to blur without which this feature does not seem to work).

I have not tested this much with respect to slider groupings. But I think it would be good to start adding at least some basic support for price fields because it is another common integer style field type.