Add price-set region and allow templates & html to be prepended

This proposal is in 2 parts

1) add region price-set-1
2) alter region code to allow prepending as well as appending to the region

Note that at the moment it is only possible to have one priceset on a page but I thought it might be worth appending the '-1' incase in future more than one is possible.

For front end forms the placement of the discount code makes most sense directly before the price-set (where relevant) & hence I think the 'before' option makes sense in a region