Create sales_region scaffold and move it to admin.
Create sales_agent scaffold and move it to admin.
Create the association to sales_agent model for sales_region model.
Convert id to sales_region object in admin/sales_agents controller.
Create shipment scaffold and move it to admin.
Create payment scaffold and move it to admin.
Add has_many association with payment model to sales_order model.
Create the association between sales_agent model and sales_order model.
Replace the sales_agent column with a references column.
Update pages in order to show sales_agent name.
Add the association between sales_order model and sales_region model.