Make ExportQueue and CollisionFreeMap data human-readable by "fluo scan" command

[mikewalch]

When users decide to use an the ExportQueue or CollisionFreeMap recipe, the underlying data is stored in a Fluo table in serialized form. This makes it hard for users to view this data when scanning their Fluo table. It would be nice if these recipes provide plugins that made this data human-readable when scanning the Fluo table.

[keith-turner]

Opened apache/fluo#568. This will make it possible to see the raw data more easily. I am still thinking of doing something at a higher level in fluo recipes that makes it possible to see the de-serialized data.

I was thinking of having a Printer registry where recipes could register a range and a class to print keys in that range. This would be stored in config. Then utility code could use this registry to scan the table calling specialized code to print different ranges of the table. This would be similar to the TransientRegistry

[keith-turner]

With the new fluo exec command, could probably provide a command line utility that would print data in a collision free map.