GEOMESA-281 Create a strategy decider function

refactored to create a Decider that decides on Strategy (attribute index, spatiotemporal index or id index)
Strategy executes the query
this will be the framework upon which more complicated cost analysis of query planning is based
As a general discussion point, I'm tempted to suggest breaking this file up.  
We could have Strategy.scala, STIdxStrategy, AttributeStrategy, and RecordStrategy.  

Thoughts?