2014-07-23 ago clarified module name: facilitate alternative GUI frameworks;
2013-04-04 ago separate module "GUI", to keep this out of the way of generic Isabelle_System operations, notably for non-Isabelle/jEdit applications;
2013-03-07 ago avoid -Infinity which confuses JFreeChart histogram;
2013-02-22 ago updated headers;
2013-01-20 ago accomodate scala-2.9.2;
2013-01-18 ago use inlined session name as title for charts;
2013-01-18 ago charts for future task runtime statistics;