Improve locations_list accessor a little bit

Hey guys this a follow up of https://github.com/RevolutionPrep/netsuite/commit/223b2481c00f18a9cc138956850865562a5c3242. I didn't mean to push that commit at the time sorry. This still doesn't look ideal but helps a bit to access the locations list. We can do `item.locations_list.locations` instead of `items.locations_list.attributes[:locations]`. Just like it's already done with the PricingMatrix example.

Ideally I'd love to get the locations_list with only `item.locations_list`. But I think I might have to change a bit more code on Actions::Search.