GEOMESA-121 Rewrite input filters with ORs at top.

* Implemented rewriting arbitrary filters in Disjunctive Normal Form.
  This means that any ORs have been 'bubbled up', and any NOTs have been 'pushed down'.

  The resulting filter tree has at most one OR at the very top.
  Additionally, each child of that OR is an AND or a base filter.

* Implemented property-based tests for the filter rewriting functionality using ScalaCheck.

Of note:  A clear optimization is that attribute filters need not be split up or otherwise mangled.
This issue is as https://geomesa.atlassian.net/browse/GEOMESA-171

* Refactored some of the test code to pull data generation.
Hmm...  I was being cute here with this, and that's why I've kept it in src/test.  This implicit closes over a static FilterFactory, so if we move it to main, I'd be tempted to think about that some. 

The combinators enable pithy filter creation like this 
```
val filter = (3 || 4).! || (1 && 2)
```
in the OrSplittingFilterTest.  

Anyhow, since the code is only supporting tests at the minute, I have it here.