Label for Metadata within Bolt Array RDD

[SteveAIS]

It would be nice if we had the ability to store metadata as a text value in the key of the Bolt Array RDD. It's currently a singleton tuple i.e. "(1,)" so the second half of that tuple could be used to store metadata as a string (e.g. JSON). That would allow Spark commands to be used against the RDD to further filter your image set by metadata values, such as a lat/lon or a date/time.