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

lib/PayPal/Api/RedirectUrls.php

@@ -23,8 +23,7 @@ class RedirectUrls extends PPModel
      */
     public function setReturnUrl($return_url)
     {
-        if(filter_var($return_url, FILTER_VALIDATE_URL) === false)
-        {
+        if (filter_var($return_url, FILTER_VALIDATE_URL) === false) {
             throw new \InvalidArgumentException("Return URL is not a fully qualified URL");
         }
 
@@ -84,8 +83,7 @@ class RedirectUrls extends PPModel
      */
     public function setCancelUrl($cancel_url)
     {
-        if(filter_var($cancel_url, FILTER_VALIDATE_URL) === false)
-        {
+        if (filter_var($cancel_url, FILTER_VALIDATE_URL) === false) {
             throw new \InvalidArgumentException("Cancel URL is not a fully qualified URL");
         }
         $this->cancel_url = $cancel_url;
@@ -120,7 +118,7 @@ class RedirectUrls extends PPModel
 
         return $this;
     }
-    
+
     /**
      * Get Cancel URL
      * Url where the payer would be redirected to after canceling the payment