[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. 
I'm not sure, but do we need libmagickwand as a build dependency?

I heard some avatar-related things need image magick. But any avatar-related computation happens *after* the package was built. I know no place where we need image magick during the package build (although it might be that something needs it during asset precompilation).

So, the dependency needs either to be moved to `dependencies` or needs to be removed.