Add data tags to price field options

Hi Coleman, I wanted to get your feedback on this, after briefly discussing with Tim on IRC. I don't deal with price sets via js much but when others do there always seems to be much cussing about classes & html structure. I just needed to do some & it seemed to me that adding data classes to the html was potentially a fix. In the case of the piece I was working on I want to know the membership_type_id & num_terms of the selected option - both values in the price_field_value table.

I'll do a PR of what I think might improve this & you can feedback. The data in the table doesn't seem to be sensitive.