GEOMESA-164 Add GeoMesa Pages to GeoServer

* Adds Accumulo stats, HDFS stats and config.
* Implements ability to  initiate M/R jobs.
GEOMESA-173 Extract avro features into its own subproject

Moved AvroSimpleFeature into its own subproject.  Implemented
AvroSimpleFeatureFactory to create AvroSimpleFeatures when
using SimpleFeatureBuilder.
Merge branch 'accumulo1.4/1.x' of github.com:locationtech/geomesa into f_set_default_dtg_1.4
Refactor TemporalIndexCheck to be more concise. Also a few minor formatting changes and change the setting of
UserData in the AccumuloDataStore from a map to a foreach due to side-effects.