Integrate Visualis Widget as an appjoint node of DSS

[MountHuang]

After integrating Dashboard/Display as a node of DSS, we should further enhance the integration with Visualis by adding Widget node, which accepts a Spark-SQL node as its content, and then automatically parses and creates a View based on that SQL statement with meta-data ready. This will make users to only focus on workflow editing page and do not need to jump to Visualis page to do View level construction anymore.