API - Fix missing translation for 'invalid taxonomy id'.

Invalid taxonomy id was not translated.
Account for current_order returning 'nil' in OrdersController#update

Fixes #2750

Conflicts:
	core/config/locales/en.yml
	core/spec/controllers/spree/orders_controller_spec.rb
Replace stub! with stub.

See David Chelimsky's explanation: http://www.mail-archive.com/rspec-users@rubyforge.org/msg13270.html

Fixes #2898
Respond with a blank 204 status when deleting a taxon

Fixes #2747
only show eligible adjustments on the backend

Conflicts:
	core/app/views/spree/admin/adjustments/_adjustments_table.html.erb
Correct documentation for title helper

Fixes #2878

Conflicts:
	core/lib/spree/core/controller_helpers/common.rb
Only set ActiveMerchant::Billing::Base if gateway_options[:server] is available
Bump highline to 1.6.18
Bump ffaker to 1.15.0

This will fix a bundle conflict when I switch between 1-3-stable and master branches.
Replace tabs with spaces in config/routes.rb
Remove executable bit from core/config/routes.rb
Add missing back_to_users_list to core/config/locales/en.yml
Generate an API key for all users

This is so that we can authenticate to the API using a token always.
Introduce Spree.uri and Spree.ajax helpers

Spree.uri is just a proxy to Spree.url. I kept typing uri when I meant url, and thought people might want to do both.

Spree.ajax takes some arguments and processes the URL through Spree.url before passing it to $.ajax. This is useful for people who want to make authenticated API requests to Spree.

Conflicts:
	core/app/assets/javascripts/spree.js.coffee

Fixes #2901
Modify CreditCard#brand to use spree_cc_type, allowing development credit cards to be used

Fixes #2923
fixed error with dropdown when switching between a country with states and another country with states

Fixes #2912
Check if order has payment step before checking for @order.payment?

Fixes #2910

Conflicts:
	frontend/app/controllers/spree/checkout_controller.rb
Test for broken currency representation.
Fix active merchant for some currencies.

Currencies without 2 decimal places would not be correctly represented
to active merchant, as they would always be multiplied by 100.

As an example, something costing 200 yen would pass 20000 yen to active
merchant.

This now uses the cents from the money object which handles this logic
much better.

Fixes #2930
Fix exception when product brand is nil

Fixes #2927