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/UpdatePlan.php

@@ -0,0 +1,45 @@
+<?php
+
+// # Update a plan
+//
+// This sample code demonstrate how you can update a billing plan, as documented here at:
+// https://developer.paypal.com/webapps/developer/docs/api/#update-a-plan
+// API used:  /v1/payments/billing-plans/<Plan-Id>
+
+// ### Making Plan Active
+// This example demonstrate how you could activate the Plan.
+
+// Retrieving the Plan object from Create Plan Sample to demonstrate the List
+/** @var Plan $createdPlan */
+$createdPlan = require 'CreatePlan.php';
+
+use PayPal\Api\Plan;
+use PayPal\Api\PatchRequest;
+use PayPal\Api\Patch;
+use PayPal\Common\PPModel;
+try {
+    $patch = new Patch();
+
+    $value = new PPModel('{
+	       "state":"ACTIVE"
+	     }');
+
+    $patch->setOp('replace')
+        ->setPath('/')
+        ->setValue($value);
+    $patchRequest = new PatchRequest();
+    $patchRequest->addPatch($patch);
+
+    $createdPlan->update($patchRequest, $apiContext);
+
+    $plan = Plan::get($createdPlan->getId(), $apiContext);
+
+} catch (PayPal\Exception\PPConnectionException $ex) {
+    echo "Exception: " . $ex->getMessage() . PHP_EOL;
+    var_dump($ex->getData());
+    exit(1);
+}
+
+ResultPrinter::printResult("Updated the Plan to Active State", "Plan", $plan->getId(), $patchRequest, $plan);
+
+return $plan;