SciYAG's new plot system

Today (or rather, yesterday), I started using SciYAG at work. It did prove useful, even in the stage of non-completion in which it was. Great ! However, I found that something was missing sorely: the ability to display several curves at the same time (yes, SciYAG is only pre-alpha software...). A quick look tonight showed me that it was time to change the way plots were implemented. I therefore changed completely the structure to profit from the QGraphicsScene scheme. Attached is a result obtained with the first commit... It looks great ! QGraphicsScene is very easy to use, thanks to the Qt developers.

However, I found out that when I was switching antialiasing on, the rendering time was excessively great for big plots (around a second for 7000 points on my machine). So I decided to use OpenGL rendering. It turns out that it is as simple as this:

format = Qt::GLFormat.new()
format.set_sample_buffers(true)
@plot_view.set_viewport(Qt::GLWidget.new(format))
@plot_view.setRenderHints(Qt::Painter::Antialiasing)

Fantastic, isn't it ??