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

README.md

@@ -128,5 +128,5 @@ There are two kinds of tests that we include in our sdk package. Unit tests, and
 
    * [API Reference](https://developer.paypal.com/webapps/developer/docs/api/)
    * [Reporting issues / feature requests] (https://github.com/paypal/rest-api-sdk-php/issues)
-
+   * [Pizza App Using Paypal REST API] (https://github.com/paypal/rest-api-sample-app-php)
 [![Bitdeli Badge](https://d2weczhvl823v0.cloudfront.net/paypal/rest-api-sample-app-php/trend.png)](https://bitdeli.com/free "Bitdeli Badge")

composer.json

@@ -14,8 +14,7 @@
     "require": {
         "php": ">=5.3.0",
         "ext-curl": "*",
-        "ext-json": "*",
-        "paypal/sdk-core-php": "2.5.*"
+        "ext-json": "*"
     },
     "require-dev": {
         "phpunit/phpunit": "3.7.*"