Fix shipping methods showing up multiple times in admin
Switch the mailers to be invoked using ids, not model objects. This makes it easier to support asynchronous mail jobs, as only simple ids need to be persisted.

Fixes #2808
Better factory integration for extensions.

Related to #2780
Update extension README, detailing new factories integration.

Related to #2780
Find visible select2-input element within promotion_adjustments_spec
Select correct element in order_details_spec to alter the quantity of

This test was working for SQLite, but in MySQL+PostgreSQL the order was different, causing the test to break.
Target correct element in stock_managment_spec

This test worked in SQLite+MySQL, but not in PostgreSQL. This commit fixes that.
Fix incorrect syntax in products/_thumbnails for @product.variant_images
Fix issue where two 'Clothing' taxons were being created in taxons_spec
Fix issue where, if using routing-filter, taxon autocomplete would break

Fixes #2248

This is due to the URL provided by spree.admin_search_taxons_url returning something like http://localhost:3000/admin/taxons?locale=en and then the code was appending '?ids=1' to the end of this, which is obviously an incorrect URL.

This new solution is more bulletproof.

Conflicts:
	backend/app/assets/javascripts/admin/spree_backend.js
	backend/app/assets/javascripts/admin/taxon_autocomplete.js.erb
	core/app/views/spree/admin/shared/_routes.html.erb
Add update only shared example.

Fixes #2861
Fixes #2788 allowing use of config.threadsafe!

Fixes #2852
Should not use dom id new_product twice.

Fixes #2852
Use fully-qualified constant when referencing Package within Spree::Stock::Splitter::Base

Fixes #2832
Fixed prototype add fields selector

Fixes #2761
Don't configure ActionMailer settings if they're already configured

Fixes #2855
fixes jstree ordering problem with jquery 1.9

Fixes #2728
Bump Money to 5.1.1

Contains a fix for this bug: https://github.com/RubyMoney/money/issues/271
ActionMailer::Base.smtp_settings in MailSettings spec
Use lazily_find_element in order_details_spec rather than sleep