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
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