[api] Orders responses now contain the checkout_steps

This is so that API clients have an easy way of listing the available steps for the order, indicating what step they're up to and that sort of thing.
Order transitions should be attempted when on the edit page

Fixes #3336
added support for shipments on order creation through api
Ask people for complete Gemfiles when posting issues.
Fix wrong discount calculation with flat percent promotions when there are more than one line item in the order

Fixes #3054
Add default order to the variants_including_master product association
Translation fix in StockTransfersController. Make back to transfers buttons consistent.

Fixes #3362
Remove optimistic lock from inventory units.

Fixes #3238
Fixes #3367
Show useful error messages for promotion rules and actions

Fixes #3358
Bump rspec-rails to 2.14.0

Fixes #3356
Update Font Awesome to version 3.2.1 with 361 icons total now available in admin

Fixes #3355
Remove items with quantity 0 on cart page

Read line removed in e07f4569f2dd63f411d81b6cf380140a73ac1de1 and add
spec to prove why it needs to be there for now

Fixes #3353
Generate sensibly lengthed SKUs
Add ability to convert Spree::CreditCard objects into ActiveMerchant::Billing::CreditCard objects

This is because some gateways, such as USA EPay, will only take a AM::Billing::CreditCard object.

See here: https://github.com/Shopify/active_merchant/blob/7451976878ee35bdb753e905ccd9a833af0d1a5d/lib/active_merchant/billing/gateways/usa_epay_advanced.rb#L1296

Conflicts:
	core/spec/models/credit_card_spec.rb

Conflicts:
	core/spec/models/credit_card_spec.rb
Merge branch 'master' into rails4-on-master

Conflicts:
	core/app/models/spree/order.rb
	frontend/app/controllers/spree/orders_controller.rb
	frontend/spec/controllers/spree/orders_controller_spec.rb
Fix Product has_many :variants_including_master definition