Bugfix: Always Submit Selected Shipping Method on Update Checkout

Fixes a bug where the shipping method was not posted on update checkout
if only a single shipping method is available (it's a hidden input
rather than a select or radio group)
Merge pull request #3326 from justinstern/master

Bugfix: Always Submit Selected Shipping Method on Update Checkout
Change is_visible for variations to make method calls cleaner.
Remove need for pre-ambles - standardize hooks. Closes #3181.
Checkout js
No add to cart redirect, and use POST for add-to-cart Closes #3200
kill helper closes #3332
New dummy data #3119
Enforce session as array data, and settings api tweak for special chars. Closes #3135.
Fixed my merge gone bad
Readme for cross sells merge fix
Fixed posting shipping method when only one is available

As committed on master branch:
- https://github.com/woothemes/woocommerce/commit/d8ba734d4f71a050df82947d2a8184f7dd8e515d
Fixed query breaking when using some product widgets and closes #3333
Tab filters. Closes #2786.
Review nonce. Closes #3324.
Adding translatable page title to download file error page
CZ lang completed

CZ lang completely translated.
Added needed states for Spain
Update woocommerce-es_ES.po

Updated untranslated strings, countries and currencies, and fuzzy translations.
Merge pull request #3345 from jbermudez/patch-1

Update woocommerce-es_ES.po