pom.xml: upgrade metrics to 3.0.2

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
pom.xml: add dependencies for killbill-skeleton

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
pom.xml: fix groupId for Ning's maven plugins

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