Support for collection based port in Apex

[Chinmay Kolhatkar]

Hi,

This is coming from https://github.com/apache/incubator-apex-malhar/pull/142

The code changes uses ports wrapped in the collections.
Currently Apex does not support collection of ports.

But, I think this is a good idea to support for the use cases where the
number of ports are not know upfront.

Thoughts?

~ Chinmay.