GEOMESA-330 Avro SimpleFeature's getProperty should return a Property even when the value is null

This addresses an issue found by a user who was attempting to run the Quick Start tutorial.
GEOMESA-328 Fix IndexIterator exception
 * The fix is from @anthony-ccri.
 * The tests show the exceptions which we observed on tablet servers.
WIP - Release 1.0 tarball

Running with mvn package -P assemble now generates a tarball under geomesa-assemble/target. Further instructions
are found in the GeoMesa tools README.
use our own license
updates to README
small changes to make bundling the tarball better and easier
adding ability to override instanceName and zookeepers
changing to HADOOP_CONF_DIR and updating accumulo dependency to be provided
splitting export up in geomesa-tools and updating pom
no longer including shaded jars, including dependencies, adding debug option to geomesa shell wrapper
removing unnecessary env variable