Added the code to plot the actual Graph.

This version already plots the dive-graph, with the
gradient and all that jazz. One thing that will be
easily spotted is that the size of the line is very
thick - easily changed, I'm just using the default.
As soon as everything is plotted correctly I'll
fix the lines.

Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>