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
Enabling Future Payments

- Added feature to create future payments
- Updated Authentication model to retrieve long lived refresh token
- Updated Documentation
- Updated Sample