Only set display_name in OrderPopulator#check_stock_level when it's needed

This should speed up in_stock query checking, as it's no longer querying option_values + option_types tables as well.
Move Error Text calculation inside error block
Fixed bad style escaping within admin/products/index.html.erb

Fixes #3439
Do not check stock quantity twice when saving line item

Every time an user pressed the add to cart button spree was checking
stock in OrderPopulator and before saving the line item, through
Stock::AvailabilityValidator. I believe we only need to check stock on
the LineItem model

Fixes #3434

Conflicts:
	core/app/models/spree/order_populator.rb
Remove ControllerHelpers::SSL `force_ssl_redirect`

Turns out that Rails 4 introduced a `force_ssl_redirect` as well and
so that method got overriden from within spree core. The spree
implementation however expected the only param passed to be a string or
something that we could assign :host and on Rails ForceSSL a hash is
given instead so this statement would be true

    redirect_options.merge!(:host => host) if host

and users would get the error described in https://github.com/spree/spree/issues/3283

Here's the current Rails ForceSSL implementation https://github.com/rails/rails/blob/v4.0.0/actionpack/lib/action_controller/metal/force_ssl.rb#L66
and in 3.2.14 https://github.com/rails/rails/blob/v3.2.14/actionpack/lib/action_controller/metal/force_ssl.rb

Removing the `force_ssl_redirect` from spree core seems to fix the issue
as that method was just a copy of the old implementation of Rails
`force_ssl` which is already called from spree SSL module

Remove spec setting application.config.force_ssl true

It doesn't represent a valid use case. By the time that code is run
the application is already initialized so that really doesn't make any
difference. We would have to add `force_ssl` inside the
ProductsController class to make the spec pass, only that it breaks
other specs so I believe we'd rather remove it

In Rails 4 SSL application wide is taken care of a middleware called
ActionDispatch::SSL which is included on the app load. Looks like
`force_ssl` is only used on the Controller level
Add validation of shipping_category_id to Product. Fixes #3188
README fix - use example that's still relevant
Remove select2-rails from Rails frontend gem

Bump select2-rails to ~> 3.4.1 in backend gem

Update helper `select2_search` implementation due to latest changes on
select2 generated markup, had to find a new way to grab select2 element
id

Fixes #3457
Remove rails from frontend and backend gemspecs.
Remove deface from frontend and backend gemspecs.
index spree_orders#completed_at
Add option_values to variant template [api]

Fixes #3460

Conflicts:
	api/app/views/spree/api/variants/variant.v1.rabl
	api/spec/controllers/spree/api/states_controller_spec.rb
Added :user at :tab was missing in I18N

Fixes #3455
Move font-awesome into app/assets for scss import. Fixes #3465
Fix `load_sample`

Broke after 7a5e43662c57807dafaebf8160069e4de8f1c855 which requires
product to have a shipping category

Add build for spree/sample load data task
Add Sample to build.sh
No need to call accessible_by again in ProductsController, as it is already done in BaseController's product_scope
Bump coffee-rails and sass-rails dependencies to 4.0.0
Use paranoia for deleted_at functionality

Fixes #3321

Conflicts:
	core/CHANGELOG.md
	core/app/models/spree/product.rb
	core/app/models/spree/tax_category.rb
	core/app/models/spree/variant.rb
Bump awesome_nested_set to 3.0 rc

Fixes #3472