Remove unused Admin::PropertiesController
Remove Spree::Core::Responder

To my knowledge, this isn't actually used anywhere in any Spree store, ever.

There are much better ways to implement this functionality than overriding respond_with in such a messy way.
Remove require for spree/core/responder
Must use spree.* prefix for routes inside CheckoutController

This is because CheckoutController's spec was failing
Undo respond_with removals.

This is causing two problems.

The first is that all URLs inside controllers, helpers and views are now needed to be prefixed with the spree routing helper. This is not necessary, as you can see from [this line][1] within Forem.

The second problem is that URLs *without* this prefix can cause the tests memory consumption to balloon and consume all the memory on the machine. This is why the Travis tests were being killed: https://travis-ci.org/#!/spree/spree/jobs/2969163

[1]: https://github.com/radar/forem/blob/2fcf21adf1d4e44e2311862b035c79f2660b4a76/app/controllers/forem/admin/forums_controller.rb#L18

This is a combination of 4 reversion commits.
Revert "Remove respond_with helper"

This reverts commit e1920f638b498964bd58fe79e3c269ad4d8f5a1d.

Revert "Remove respond_{to/with} calls from controllers that don't need them"

This reverts commit 4e0249dbaa8d31d682bc9133f53411fe57aab3b5.

Conflicts:

	core/app/controllers/spree/checkout_controller.rb
	core/app/controllers/spree/orders_controller.rb

Revert "Remove Spree::Core::Responder"

This reverts commit 992683015986e3a899f4ced70a55a5f8b0f93b6f.

Revert "Remove require for spree/core/responder"

This reverts commit dab1528d9d8e3b39f221a189691d4994e19b4cd8.
Merge branch 'master' of https://github.com/spree/spree

* 'master' of https://github.com/spree/spree: (88 commits)
  The order object within associate_user may be current_order as well, not just @order
  [dash] Add missing end to Admin::AnalyticsController
  Always pass Spree::Payment's currency to gateway
  Taxonomies now have a position attribute
  refactor : update_positions
  fix datepicker format
  [dash] Use correct flash messages within analytics controller
  Fix translations in admin backend
  Add currency support to models.
  Validate format of email only if present
  [api] Fix view_version_extraction_strategy for versioncake config
  Localize datepicker date format
  Scope thumbnails lookup in product.js.coffee
  Removed record_log, a duplicate logging function The record_log method is not being used anywhere within Payment model and it duplicates the record_response method.
  Use versioncake for versioning of API resources
  Set Rabl config not to return json root or child root
  Fix order column for variants association
  use the name of the option type instead of the presentation. That way different option types with the same presentation are easily spotted.
  Fix issue when attempting to move taxon to the bottom of the tree
  Move font-awesome around in the asset pipeline.
  ...

Conflicts:
	core/app/controllers/spree/admin/reports_controller.rb
	core/app/controllers/spree/checkout_controller.rb
Merge branch 'master' of https://github.com/spree/spree

* 'master' of https://github.com/spree/spree: (85 commits)
  Add fix for - old country id for new state (#2260)
  Refactor checkouts/edit.js customer picker code
  Fix usage of t Handlebar helper within variants/_autocomplete
  escape javascript in ecommerce tracking code
  Ensure there is always a complete step returned in checkout_steps
  [promo] Fix user picker
  Programmatically select2 a field within admin/products/edit/variants_spec
  Set select2 fields in configuration/states_spec programmatically
  Set select2 fields within shipping_methods_spec tests programmatically
  Don't disable select2 in test env
  Improve select2 capybara_ext helper to work with select2 boxes that can contain multiple values
  Update license.md
  [api] Set default format to json
  [api] Move Spree::Api::Responders require to spree_api.rb
  Delete unused this_file_language translation
  Add taxon placeholder translation
  Switch customer autocomplete in admin backend to use Select2
  Alias firstname <=> first_name & lastname <=> last_name in Address model
  Only transition to complete if payment is required and there is a payments record OR if there is no payment required
  Refactor .travis.yml
  ...
Remove unneeded preloading of preferences
[api] Fix 1.8 syntax error in Api::V1::BaseController
Fix 1.8 incompatibility with Time.new in base_helper_spec

Related to #2405
make new product button always visible on edit product page.

I found that it will be very useful when entering products through admin side. this will allow use to quickly navigate to product page after adding new one without going back to product list

Fixes #2407
Namespace OrderPopulator reference in OrdersController so people don't run into potential issue where it would attempt to lookup a top-level OrderPopulator class
Fixed hardcoded paths to fontawesome

Fixes #2424
Remove unused translation for no_items_in_cart + order_confirmation_note
Switched decorator loading to the decorators gem.

Part of #2415
Moved decorators under the app/decorators convention.

Part of #2415
Moved Spree::StoreController class_eval from engine to store_controller_decorator.

Part of #2415
Revert changes from #1981

This is due to sbounmy suggesting it could be useful:
https://github.com/spree/spree/issues/1981#issuecomment-11682782
Use available? and acknowledge allow_backorders setting in OrderPopulator

Fixes #2430
[api] Remove api/v1 directory, move inventory_units controller to correct spot