Create test orders on live sites

[jedateach]

Sometimes developers or shop admins need to place a test order on the live site. The problem is that they don't want to make actual payment in the process, and don't want to mess up existing orders. Sometimes orders can be placed on a test site, but it can be hard to manage a test version of a site.

Experimental work started here: https://github.com/burnbright/silverstripe-shop-testorders