Just stumpled across this old question with no answer and i like to try...
I get this working when adding a few lines in clientBilling.inc:
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
xmlns:ui="http://xmlns.jcp.org/jsf/facelets"
xmlns:p="http://primefaces.org/ui">
<p:tab title="other tab">
</p:tab>
<p:tab title="another tab">
</p:tab>
</ui:composition>