2.1

A bunch of changes I've been meaning to make for a while:
 * Allow adding extra information to a registration payload in an extensible and semi-safe way
 * Update to jetty 9 and apache-curator 2.6
 * Provide the ability to run servlets through socrata-http-jetty
 * Make socrata-http-jetty and socrata-http-client's configuration extensible in a way that's easy to keep binary compatibility
 * Allow socrata-http-jetty to NOT hook signals (intended for use with an embedded Jolokia)