Add workflow with Fulfillment

Problem/Motivation

When handling orders of physical / shippable goods it comes in handy to have orders in the fulfillment state to indicate that shipping isn't done yet. This is true for recurring orders of such type, so we should introduce a workflow for this too, as the regular workflow, provided by commerce, isn't exactly compatible with recurring orders.

Proposed resolution

Add additional workflow so the use case can be covered.