Configurable shipping options and rates per vendor

[mariannk]

It would be good if each vendor can configure own shipping methods (options) and buyers whose orders contains items from several vendors could select vendor-specific shipping options at checkout.

Or allow vendors to choose pre-defined shipping method

By the way, warehouse support is already added. We can add a new warehouse for each vendor and simply configure rates for each origin (warehouse)

also see https://github.com/nopSolutions/nopCommerce/issues/1928