* YUV plane with Y varying can be exported (ratio U:V fixed)
* RGB plane with two components on one and one component on other axis can be exported
  Usage: e.g. for Curves widget, to visualize color changes
Vectorscope changes:
* Realtime factor shown
* Pixel brightness relative to image size for Green (still needs to be tweaked)

svn path=/trunk/kdenlive/; revision=4587