2.0.0.0-dev65

* Fixed bugs:
  * Fixed inability to execute System Backup, Database Backup, and Media Backup
* Indexer implementation:
  * Implemented a new optimized Catalog Category Flat Indexer
* Cron improvements:
  * Added the ability to divide cron tasks into groups
  * Added the ability to run cron groups in separate processes
* Caching improvements:
  * Added a new mechanism to identify uniquely page content (hash-key for cache storage)
  * Added a tab for Page Cache mechanism in System Configuration
  * Implemented the ability to configure the Varnish caching server settings and download it as a .vcl file
* LESS pre-processing to CSS
  * LESS files in library, theme, module are automatically compiled to CSS during materialization
  * LESS files compilation caching mechanism added in Developer mode
* Modularity improvements:
  * Moved the Shortcut Buttons abstraction from PayPal to Catalog
  * Moved the Recurring Profile functionality to a separate module
  * Moved the Billing Agreements functionality to the PayPal module
* Improvements in code coverage calculation:
  * Added code coverage calculation in the clover xml format for unit tests
* GitHub requests:
 * [#377] (https://github.com/magento/magento2/issues/377) Remove and avoid javascript eval() calls
 * [#319] (https://github.com/magento/magento2/issues/319) No message was displayed when product added to shopping cart.
 * [#367] (https://github.com/magento/magento2/issues/367) Improve the error message from the contact form
 * [#469] (https://github.com/magento/magento2/issues/469) Can't change prices on different websites for custom options
* Updated the Customer service exception handling, and added tests
* Added usage of the Customer service to the Customer module, replacing some direct usage of the Customer model
* Updated various PHPDoc with the parameter and return types