[WIP] Build OpenProject release 3.0.X deb package via packager.io

This PR is not meant to be merged right now. It is created for early testing on travis only. 
@tessi right we can set environment variables and configure openproject. But in regard to packager I like having a configuration file available. This supports the idea of documenting what is going on and were packager is involved. I would also like to stick to this right now.