pom.xml: updates for release 0.19.16
pom.xml: updates for release 0.19.16

Catalog api cleanup and enhancements for mutli-versions
Fix missing fields in invoice items and remove constraint for generating stricly positive external charges

Signed-off-by: Kill Bill core team <1a73af9e7ae00182733b2292511b814be66f065f@killbill.io>

sbrossie/killbill,killbill/killbill,killbill/killbill,sbrossie/killbill,killbill/killbill,sbrossie/killbill,killbill/killbill,killbill/killbill,sbrossie/killbill,sbrossie/killbill