GEOMESA-373,GEOMSA-374,GEOMESA-375,GEOMESA-376

* fixing plugin to remove unnecessary dependencies
* moving all logging to log4j & slf4j via scalalogging since mini accumulo (used in tests) must use log4j and not logback
* shading guava and apache commons projects into geomesa-plugin uber jar so that existing geoserver jars don't need to be removed
* upgrading geoserver to 2.5.2 to match geotools 11.2
GEOMESA-364 AvroSimpleFeature Writer

Created a new AvroSimpleFeatureWriter to implement Avro DatumWriter. Changes include:
* AvroSimpleFeature objects no longer have expensive initialization
* SimpleFeatureEncoders now are parameterized by SimpleFeatureType
* LoadingCaches converted to instance variables for type mapping
* AvroSimpleFeatureWriter handles writing instead of AvroSimpleFeature.write() method
* Reuse DirectBinaryEncoder/DirectBinaryDecoder for performance (no buffering) on read/write
* Reuse ByteArrayOutputStreams on write
* Serialization method handles any SimpleFeature type (not just ASF)
* Use cached sft.indexOf() method instead of caching via LoadingCache