2.0.0.0-dev53

* Moved general action-related functionality to \Magento\App\Action\Action in the library. Removed Magento\Core\Controller\Varien\Action and related logic from the Magento_Core module
* Moved view-related methods from action interface to \Magento\App\ViewInterface with corresponding implementation
* Moved redirect creation logic from the action interface to \Magento\App\Response\RedirectInterface
* Moved Magento\Core common blocks to the library
* Added reading of etc/integration/config.xml and etc/integration/api.xml files for API Integrations
* Various improvements:
  * Email-related logic from the Core and Adminhtml modules consolidated in the new Email module
* GitHub requests:
  * [#238](https://github.com/magento/magento2/pull/238) -- Improve escaping HTML entities in URL
  * [#199](https://github.com/magento/magento2/pull/199) -- Replaced function calls to array_push with adding the elements directly
  * [#182](https://github.com/magento/magento2/pull/182) -- By default use collection _idFieldName for toOption* methods.
  * [#233](https://github.com/magento/magento2/pull/233) -- Google Rich Snippet Code
  * [#339](https://github.com/magento/magento2/pull/339) -- Correcting 'cahce' typo in documentation.
  * [#232](https://github.com/magento/magento2/pull/232) -- Update app/code/core/Mage/Checkout/controllers/CartController.php (fix issue #27632)
* Fixed bugs:
  * Fixed JavaScript error when printing orders from the frontend
  * Fixed Captcha problems on various forms when Captcha is enabled on the frontend
  * Fixed "Page not found" on category page if setting "Add Store Code to Urls" to "Yes" in the backend config
  * Fixed Fatal error when creating shipping label for returns