add "comment" to 2pack file

idea from https://wiki.idempiere.org/en/Developing_Plug-Ins_-_2Pack_-_Pack_In/Out#improved_Incremental2PackActivator

disscus to implement at http://www.globalqss.com/idempiere/irclog/%23idempiere.2019-11-14.log.html

open to use maven artifact for improve version order, parsing