Kenshoo integration

I've implemented the `completedOrder` handler. The other events are still a bit unclear (see comments in #76).

Also, the "Live tracking" fields will probably require access to documentation (`kw`, `GCID` and `product` no idea what to send there - maybe just `track.proxy('properties.kw') || ''` would do?); all the examples I've found leave them empty but I haven't found any that would actually fire a `completed order` event.