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/Exception/PPInvalidCredentialExceptionTest.php

@@ -0,0 +1,40 @@
+<?php
+use PayPal\Exception\PPInvalidCredentialException;
+/**
+ * Test class for PPInvalidCredentialException.
+ *
+ */
+class PPInvalidCredentialExceptionTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @var PPInvalidCredentialException
+     */
+    protected $object;
+
+    /**
+     * Sets up the fixture, for example, opens a network connection.
+     * This method is called before a test is executed.
+     */
+    protected function setUp()
+    {
+        $this->object = new PPInvalidCredentialException;
+    }
+
+    /**
+     * Tears down the fixture, for example, closes a network connection.
+     * This method is called after a test is executed.
+     */
+    protected function tearDown()
+    {
+    }
+
+    /**
+     * @test
+     */
+    public function testErrorMessage()
+    {
+      $msg = $this->object->errorMessage();
+      $this->assertContains('Error on line', $msg);
+    }
+}
+?>