Use I18n for variants on product creation prototype listing

Fixes #3844
Give us a chance to skip adjustments on order import via api

Since adjustments is tightly coupled with line items creation we can
only do that by destroying tax adjustment after line items are created.
Add :send_core_emails config prefernce

Allow developers to use standard rails mail configuration (in config
files) by setting :override_actionmailer_config to false without sending
spree core emails (e.g. order confirmation). This is useful e.g. in the
case where devs have opted to use an external mail API such as Mandrill
for store-related emails but still want to use ActionMailer in other
parts of their app.

Fixes #3812
Use sRGB colorspace

Fixes #3843
Fixes #3104
Use `unscoped` when create stock items in migration

By the time the migration runs the default scope with deleted_at was
already defined so mocking acts_as_paranoid doesn't make any difference

related to #3805
Ensure that preference keys are not prefixed with '/' if ENV['RAILS_CACHE_KEY'] is not set

Fixes #3831
remove extra include for Search module in Spree::BaseController

Fixes #3852
[frontend] remove redundant via in routes

Fixes #3853
Add changelogs for 2.1.2
[api] Add assurances that line item prices cannot be set while creating or updating orders
Add note about #3812 to core's CHANGELOG
centering search field on select2 plugin in admin area

Fixes #3854
Fixes #3842
Fix format of price input in products/new.html.erb
Use asset pipeline for jstree

Hard-coding links to /assets/ without fingerprints does not work on Rails 4
Remove version number from font awesome

The version number in the query string is not necessary for fingerprinted assets.

I'm not sure about the purpose of the #iefix anchor so I've left it in.

Additionally, some web servers do not handle query strings very well, such as SimpleHTTPServer.
[frontend] Stop people encountering uninitialized Taxon errors when they override ProductsController#show
Non-GET requests that would usually non-ssl-redirect will now respond with HTTP status 426

Conflicts:
	core/spec/lib/spree/core/controller_helpers/ssl_spec.rb
Include exception message from Spree::Core::GatewayErrors

This makes the error messages when payments fail slightly less vague than they used to be.

Fixes #3851
Bump activemerchant to 1.39.2
Clean up checks to avoid db connection on precompile

We still need to deal with the Preference / Config issue as stated in #3833