Only count eligible promotions towards Promotion#credits

Fixes #4120

Conflicts:
	core/app/models/spree/promotion.rb
[api] Split taxon_ids as they're passed to Products#create and Products#update
make sure we do the line_item adjustment check before rendering the adjustment

Fixes #4122
Fixes #4130
fix backend layout assets tags

Fixes #4127
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
Flush out association between payment and its method.

Change-Id: I7ae6a6071ad9959eacb48bda75061e58236e674f
Test against Ruby 2.1.0 in Travis
Add inverse_of to models

Fixes #4146
Revert "Make sure that api requires authentication by default"

This reverts commit 3e89c8e52ced3935f74048f288aa9cdc524c88dc.

This is causing issues with the frontend & backend builds that need to be fixed before this commit can be applied.
Add CHANGELOG entry for js responder security fix