Add index to Spree::User.spree_api_key

Fixes #3884
Updated docstring explaining how to include controller requests test support in rspec.

Fixes #3898
Fixed Spree::Api::ProductsController#index to accept multiple ids

Fixes #3886
Relax money dependency
Bugfix: Taxons could not be ordered

If you reorder the taxons in the admin interface, it does not
have any effect, because the ordering of the taxons is not
used. Setting a default scope with this ordering fixes that.

Fixes #3891
Fixes #3833
Fixes #3390
Spree::Payment.class.undescore will always convert spree/payment

Fixes #3889

Conflicts:
	backend/app/views/spree/admin/payments/show.html.erb
Fix fieldset not resizing on some @media sizes.

Fixes #3871
Fixes #3890
[api] Don't depend on ordering in taxons_controller_spec
[api] Add missing per_page node to products/index
Clear out entries from CHANGELOGs
Use evaluate_script instead of execute_script

evaluate_script was meant to be used for these kinds of situations.

Fixes #3894
Clarify how spree accepts pull requests, may need to be cross committed to the docs in spree-guides is support for the change is present.

Discussed in #3894
Specify class name for users association in Promotion::Rules::User
Update option_type for has_many product through

Needed for search from option value.

Fixes #3910
Added Kaminari call to add rel next/prev to head

Fixes #3903
Bump activemerchant to 1.41.0
Persist search fields across requests for sales total report

Fixes #3906
Make product variants thumbnails selection more specific in JS
Sorts country list correctly with accents

Fixes #3911
Reference address html elements by id only