Allow trades to be a vector

[nuclearkatie]

Right now, trades have to be a single resource (material or product). In order to implement packaging, trades need to be allowed to be vectors (and potentially vectors of vectors for transport units...)

Or maybe, offers to requests need to be allowed to be vectors. Then, trades can still be single resource, but the DRE would have to be able to compare multi-pronged offers to regular, single resource offers, and multiple trades could result from a single request
(now that I'm writing it out, the second one seems more complicated)

[gonuke]

(capturing some in-person discussion) - This specifically necessary in the step of executing a trade when the trade negotiation in the DRE may not have been for a specific number of packages, but the trade will be executed as a specific number of packages. Thankfully, it should not have any bearing on the mathematical definition of the problem being solved by the DRE.