Enabled Billing Plans and Agreements APIs

- Added API Classes, Samples, and Tests
- Updated Functional Tests
- Updated Documentation with new SDK Name
- Updated Few Samples to use newer nicer result page

sample/billing/GetBillingAgreement.php

@@ -0,0 +1,25 @@
+<?php
+
+// # Get Billing Agreement Sample
+//
+// This sample code demonstrate how you can get a billing agreement, as documented here at:
+// https://developer.paypal.com/webapps/developer/docs/api/#retrieve-an-agreement
+// API used: /v1/payments/billing-agreements/<Agreement-Id>
+
+// Retrieving the Agreement object from Create Agreement From Credit Card Sample
+/** @var Agreement $createdAgreement */
+$createdAgreement = require 'CreateBillingAgreementWithCreditCard.php';
+
+use PayPal\Api\Agreement;
+
+try {
+    $agreement = Agreement::get($createdAgreement->getId(), $apiContext);
+} catch (PayPal\Exception\PPConnectionException $ex) {
+    echo "Exception: " . $ex->getMessage() . PHP_EOL;
+    var_dump($ex->getData());
+    exit(1);
+}
+
+ResultPrinter::printResult("Retrieved an Agreement", "Agreement", $agreement->getId(), $createdAgreement->getId(), $agreement);
+
+return $agreement;