pom.xml: upgrade jetty-console-maven-plugin to 1.55

The upstream artifact groupId seems to actually be org.simplericity.jettyconsole.

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
pom.xml: update killbill artifacts

* Update killbill-client-java to 0.0.14
* Update killbill-commons to 0.2.21

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>