Make crucial methods in NodeLinkTreeLayout protected so that we can provide our custom layout calculations, made Params a top level class because of interoperability issues with Scala

Fix for compatibility with Scala and a getter added to layout

fix #3048039

publishing setup

going back to explicit prefuse-core subproject publishing

ok, this is bit of a hackery, but sbt publish(-local) seems to do what i want now.

tests compile

proper readme

demos all work

demo cleanup

initial commit