Make jetty version consistent with airlift pom
Add io.airlift:slice:0.5 to dependency management section

The version can be overridden via the dep.slice.version property
Update jmxutils to 1.16
Update CHANGES
[maven-release-plugin] prepare release 18
[maven-release-plugin] prepare for next development iteration
Update Jetty to 9.1.4.v20140401
Add dependencies for jetty-client and jetty-io