Remove apply button as it duplicates update buttons behavior. Discussed in issue #2720

[Closes #2776]
rspec spec -> rake spec [ci skip]
Use order.contents.add for order_spec
Fix specs by checking defined?(:config_locale) instead of respond_to?(:config_locale) which always returns false. Also refactor common controller helper to use ActiveSupport::Concern.
Fix I18n spec to check for private/protected method config_locale