GEOMESA-122 Split OR filters into multiple queries

* Created a OrSplittingFilter Visitor which helps break apart a more complex Filter into pieces.
* Moved up the SelfClosingBatchScanner into core and implemented a basic CloseableIterator trait.
No worries.  This discussion has made me feel better about my 'self'.  

Seriously, we should keep it.  Syntactically, a call to 'this' would be confusing.