v6.0.1

Main Changes to previous release version:
- Internal bugfix for file-transfer module;
- Implemented the extension module for WebRTC with the latest native extension APIs;
- Fixed the issue related to the Gradle build project;
- Synchronized with using the latest native SDK v6.0.1
- Removed the deprecated public method: Carrier.sendFriendMessage() to return value indicating as online or offline message.