By Veronika Bondarenko Order sorting is a major problem for most major retailers. When that order of pretzels or music speakers finally arrives, few think of how it got from the producer to the retailer and then to the front door — in large part because big-name retailers have so far largely kept that part of the supply chain process behind closed doors. They can be called “sortation centers,” “fulfillment hubs,” “distribution warehouses” or any number of other names but the idea is the same. This is the space where retailers like Amazon (AMZN) – Get Amazon.com Inc. Report or Walmart (WMT) – G…