Spark Integration: Streams support for Spark Jobs

Adds support to read Streams in Spark to resolve : CDAP-403

Build Running: https://builds.cask.co/browse/CDAP-DUT102-4

@anew : Please review. Thanks.
This is wrong. Calling `typeArgs[1].getClass()` will return you something like `Class.class` or `ParameterizedType.class`, which is not what we wanted. The `setStreamEventDecoder` should take a `Type`, not `Class<?>`.