2.0.0.0-dev51

* Application areas rework:
    * Single point of access to the current area code
    * Declare Application Areas
* Various improvements:
  * Breakdown of the Adminhtml module:
     * Moved the Customer-related logic to the Customer module
     * Moved the System-related logic to the Backend module
     * Moved the Checkout-related logic to the Checkout module
     * Moved the Cms-related logic to the Cms module
     * Moved the Promotions-related logic to the CatalogRule and SalesRule modules
  * Eliminated the setNode/getNode methods from Magento\Core\Model\Config and adopted all client code
  * Moved all application bootstrapping behavior to library
  * Moved application-specific behavior from the entry points to the Magento\AppInterface implementations
  * Removed the obsolete behavior from routing and front-controller
  * Refactored the route configuration loading
  * Extracted the modularity support behavior to the Magento\Module component
  * Refactored the Resource configuration loading
  * Removed the obsolete configuration loaders
  * Removed the obsolete configuration from config.xml
  * Refactored the code-generation mechanism
  * Added constructor integrity verification to the Compiler tool
  * Added strict naming rules for the auto-generated Factory and Proxy classes
  * Global functions are now called from app\functions.php
  * Removed functions.php from the Magento\Core module
  * Methods related to mageCoreErrorHandler, string and date were moved from functions.php to the Library components
  * Moved the following methods from Core Helpers to the appropriate libraries:
     * Moved the Abstract Helper to the Magento\Escaper and Magento\Filter libraries
     * Moved the String Helper to the Magento\Filter, Magento\Stdlib\String, Magento\Stdlib\ArrayUtils libraries
     * Moved the Data Helper to the Magento\Math, Magento\Filter, Magento\Convert, Magento\Encryption, Magento\Filesystem libraries and to Magento\Customer\Helper\Data libraries
     * Moved the Http Magento Helper to the Magento\HTTP library
  * The Hint Magento Helper, Http Magento Helper helpers were removed from the Magento\Core module
  * Implemented SOAP faults declaration in WSDL
  * Web API config reader was refactored to use Magento\Config\Reader\Filesystem
  * Created integrations module. Added 'Integrations Grid' and 'New/Edit' Integration pages in the admin
  * Removed obsolete page fragment code
* Fixed bugs:
  * Fixed inability to create an Invoice/Shipment/Credit Memo if the Sales Archive functionality is enabled
  * Fixed the Minimum Advertised Price link on the Product view
  * Fixed the View Files Population Tool
  * Fixed the error on saving the Google AdWords configuration
  * Fixed the error with the 'Invalid website code requested:' message appearing when enabling payment methods
  * Fixed inability to insert spaces in credit card numbers
  * Fixed inability to print orders from the frontend
  * Fixed the fatal error on removal of reviews that have ratings
  * Fixed JS error with the browser not responding when Virtual/Downloadable product are added to cart
  * Fixed inability to delete a row from the 'Order By SKU' form in Internet Explorer
  * Fixed inability to enable the Use Flat Catalog Product option
  * Fixed inability to configure Grouped and Configurable products during order creation in the backend
  * Fixed inability to insert a widget and/or a banner in CMS pages
  * Fixed inability to set the Quantity value for Gift Cards
  * Fixed the fatal error on the Customer Account > Gift Registry tab in the backend
  * Fixed inability to import with the "Customers Main File" entity type selected
  * Fixed the "Recently Viewed/Compared products" option missing on the New Frontend App Instance page
  * Fixed the fatal error on managing Shopping Cart for a customer with a placed order in the backend
  * Fixed the fatal error on an attempt to create an RMA request for Configurable products
  * Fixed error on the backend dashboard if any value except "Last 24 Hours" is chosen in the "Select Range" dropdown
  * Fixed duplicate values of options in the drop-downs on the RMA pages in the backend