GEOMESA-552, 553 Refactor GeoMesaCoverageReader to utilize functionality in geomesa-raster, create class to hold GeoMesaCoverageReader parameter values

Removed redundant code in GeoMesaCoverageReader to instead use code in the geomesa-raster project. Also moved code from geomesa-plugin to geomesa-raster to better structure and organize the project. Added a class to store GeoMesaCoverageReade GeneralParameterValues to aid in queries for raster images.
The usage of mapAsJavaMap is not needed here, as you have JavaConversions in scope and that will do the implicit conversion for you. 

Alternatively, you could instead use JavaConverters, and include the .asJava method after the definition of the Scala Map.