Fix private header dependency * removes xyplotdata_p.h dependency

Refactor current draft to fit int current design specs * fixes compilation errors * adds QChartSeries * adds QXYChartSeries * adds QXYLineChartItem * fixes xylinechart example to use QChartWidget

Test app now adds n data series of different type

Started to refactor the API to allow integrating different plot types

adds message to charts.prf

Fixed compilation on Windows

Added test data

Now using opaque circle to visualize scatter data

change function example in xylinechart example

Scatter data point now shown using a picture