Selects 'state' as default zone type when there has not yet been a selection made.  We are already showing the 'add state' button in this case, so this commit makes the UI uniform ('state' radio is selected and 'add state' button is shown)

Fixes #3432
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
Add validation of shipping_category_id to Product. Fixes #3188

Conflicts:
	api/CHANGELOG.md
	api/app/helpers/spree/api/api_helpers.rb
	api/spec/controllers/spree/api/products_controller_spec.rb
	backend/spec/features/admin/orders/shipments_spec.rb
	core/CHANGELOG.md
	core/spec/models/spree/product_spec.rb
Fix spec broken by conflict.
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
index spree_orders#completed_at
Add logo back
Correct font-awesome weirdness in admin backend

Icons for edit + delete links were incorrectly positioned and admin navbar text was very thin
Add option_values to variant template [api]

Fixes #3460
[api] Passing no parameters to ShipmentsController#update should not make it 500
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