Removing Dependency from SDK Core Project

- Copied files required for Rest API SDK
- Removed PPApiContext and directly connected APIContext with PPConfigManager
- Removed duplicate data storage of configuration and credentials.
- Code Style Fixes
- Remove build.xml file as it is not required anymore
- Updated the samples
- Updated the documentations

tests/PayPal/Test/Api/AddressTest.php

@@ -2,10 +2,10 @@
 namespace PayPal\Test\Api;
 
 use PayPal\Api\Address;
-use PayPal\Test\Constants;
 
 class AddressTest extends \PHPUnit_Framework_TestCase {
 
+    /** @var  Address */
 	private $address;
 
 	public static $line1 = "3909 Witmer Road";