joshmiller's sandbox: Commerce Stacking Dimensions

A user interface that adds a field to selected product types that track how a single product's dimensions should be increased when stacked. For example, chairs, when stacked, may only increase in height and depth by a small fraction of their single size.

Assumes Product A (with a stacking dimension field) increases in the dimensions indicate for each stacked Product A. Does not calculate if Product A fits inside Product B.

Tested with commerce_ups, should work with commerce_fedex as well. Modifies the order's total volume by changing the math on products that have a quantity of more than one and include a stacking dimension field.

NOTE: The shipping estimates, at least for UPS, and possibly for FedEx, are determined based on a "default" package size and not necessarily the product size. The default package size is set where you configure your shipping services. Since the math assumes volume, a default package of 12"x12"x12" has 1,768 cubic inches of space, and if your product is 5"x5"x5" (125 cubic inches) then you would not see a decrease in shipping estimates until you had a quantity of 15 or more in your cart. Since a volume can be any shape, that means your "default package" is not a "maximum" in any one direction, it simply defines how big of a space we have to work with, regardless of shape.