Remove Rails t() override method

Rails t() offers a couple more nice features before calling I18n.t()
see http://api.rubyonrails.org/classes/ActionView/Helpers/TranslationHelper.html#method-i-translate

And since right now we can't make Spree.t() behave the same way as Rails
t() helper we'd better let users choose t() default, in cases Spree.t()
can't cover, without throwing warnings

Fixes #3176

Fixes #3256
Explicitly declare manifest partial location so the shipment partial can be rendered in templates outside the orders folder.
include variants when loading inventory_units in Shipment#to_package

If there are 100 inventory units for a shipment, there were 100 queries for the inventory units' variants. This small alteration reduces the queries to 1.
jQuery Validate IE9 event handle fix
[API] Checkouts API update now can take line item attributes
Don't update shipping addr if use billing addr is checked

By running updateState() on shipping address form we enable those
fields and need to propagate changes from billing address to shipping
address when we shouldn't because they're already propagated server
side. We should only run updateState() on shipping form if use billing
address is not checked

Fixes #3232
Fixes #3245
Use stock_location's country for stock_location's state in stock_location factory

This is so that it doesn't create a new country and associate the state with that.
Pass a variant id as the variant_id parameter when creating inventory units in the Shipment factory.

This only took me 20 minutes to figure out. I am not a smart man.
Only create a state for a factory'd stock_location if the country doesn't already have one
Upgrade jquery-rails to ~> 3.0.0

Fixes #3203
Fixes #3237
Newer jQuery.attr returns undefined, handle gracefully
replace ids/names for select boxes as well

Fixes #3236
Added Spree::Adjustment#return_authorization scope

Fixes #3239
Display default product image when variants have none

Account for scenarios where a product has variants but they don't have
any images. In that case when displaying a variant we should check if
the product master variant doesn't have an image before displaying a
noimage file.

Fixes #3172
Fixes #3240
Added credit owed state and added awaiting return and returned states to styles

Fixes #3258
Log CVV response messages on payments

Fixes #3266
fix hardcoded paths for fontawesome

Fixes #3248
Fixing the problem with translate with relative path.

This commit fix #3176 and add #translate method to Spree module.

To fix this issue, was necessary adding a monkey patch to initialize
the i18n after load the spree base controller.

Also, I changed the method #t. Now this method is an alias to #translate.

In my concept, we need to follow the same convention of i18n and
translation helpers of rails.

So, the developers can use #t and #translate without any problems.

Fixes #3257
Fixes #3176
Not all promotions respond_to :products

Fixes #3265
Fixes #3261
[frontend] Really check for flash[:error] in orders_controller_spec, rather than setting it

Fixes #3259