new: iterator interface and improved documentation for JKQTPDatastore
reorganization of library (better separation of common code in jkqtpcommon and other code e.g. in jkqtplotter or jkqtmathtext)
- some reorganizations into different files
- additional options for graph filling (color gradients, textures, ...) as provided by QBrush
- PREPARATIONS: added a general feature to JKQTPPlotElement which allows to show a graph in a highlighted state (if supported by the derived graph class!)
- JKQTPXYParametrizedScatterGraph: added functors to transform column values into symbol type+size and line-width to give even more control
- JKQTPStepHorizontalGraph has been renamed to JKQTPSpecialLineHorizontalGraph (vertical variants also) and have gained additional features (baseline for filling and drawing of symbols)
- filled curve graphs (e.g. JKQTPSpecialLineHorizontalGraph) are now merely a specializedly initialized JKQTPSpecialLineHorizontalGraph
