[DiaCanvas] bezier curve

[Arjan M. <arj...@he...>]

I've created stuff for bezier curves. Most of the code was already
there, but it didn't do anything usefull.

I added a small screenshot. I misused the DiaCanvasBox item and added a
bezier curve inside it. Well, it's midnight while I write this, so I'll
quit.

Regards,

Arjan