GEOMESA-203 Upgrade joda-time to version 2.3

This is to streamline the IP review by the Eclipse Foundation.
It includes upgrading joda-convert to 1.6, the most recent.
GEOMESA-135 Convert ehCache to Guava cache

Removed ehCache from the DeDuplicatingIterator, as well as references to ehCache in the pom files, and replaced with Guava cache.
Removed jta dependency, fixed cache logic, and added 2 small tests

Conflicts:
	geomesa-core/pom.xml
GEOMESA-206 Update and improve README.md