Only create an order when adding a product to cart

Everytime user was authenticated an order was created by visiting any
page in frontend (if none were already associated with the current user)

Fixes #4136
Update readme for new CI location

The move of domain is permanent, according to the spreefolk in IRC
Refactor DelegateBelongsTo to not touch db on startup
show the SKU when present on the line_item.variant

Fixes #4045

Conflicts:
	backend/app/views/spree/admin/orders/_shipment_manifest.html.erb
Remove code already placed in awesome_nested_set