#3 added some features

[orbitcowboy]

Hello firends,

first of all, i was surprised about the great work that was done on wxMathPlot. It is easy to use and a great extension to the standard wxWidgets library.
During my work with wxMathPlot i faced some little limitations. The path (see attachment) contains all changes i have made:

- The (X and Y) tics colour can be set now
- When using the mpFXY class, different plot types can be set. It is now possible to plot rectangles, circles and points of different size for each layer.
- every destructor is declared as virtual and therefore prepared for intheritance.

I hope my patch (or some ideas) will find the way wxMathPlot Distribution

Many thanks and best regards

Martin

[orbitcowboy]