Look into dropping Optional from serialized data

Optional is used in some of the Recipes APIs. It also used internally. This results in slightly larger serialized data. We could drop the use of Optional internally in classes private instance var. For example [DifferenceExport.java line 49](https://github.com/fluo-io/fluo-recipes/blob/981e9accb7260767fef4c6fa906d2e3031a12ec4/modules/accumulo/src/main/java/io/fluo/recipes/accumulo/export/DifferenceExport.java#L49) uses Optional internally.

Start with DifferenceExport.java at line 49 and inspect other private instance variables that use Optional internally. Determine which internal Optional values affect serialized data, while distinguishing them from Optional values in the Recipes APIs. Done means the agreed internal uses no longer add Optional-related serialization overhead.

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