implemented graph visualization using JUNG;
added ResponseDelay trait for limiting negotiation speed;
in previous commit: refactored Actor implementing classes (like overseer and agent) by moving actors to separate classes in companion objects;
refactored agent response mechanism, see Response case class;
refactored Graph: Nodes no longer store neighbours information, instead the graph now has "edges" field;
some changes to ColoringAgent and its subclasses;
added OneTryColoring state extraction for showing nodes states in GUI;

todo: move Graph to utils;
batik and salamander visualizations are committed just for history; should be removed in next commit;