Adding simple XFlow demonstrations

-Demo1) View webcam viewfinder, take a still image snapshop, and turn
the image into grayscale

-Demo2) Same as above, but calculate and display FFT of the grayscale
image. This will demonstrate how to chain more than one operator to do
processing

-Demo3) Run webcam viewfinder feed realtime through a filter, i.e. a
grayscale transform, and display the two videos side by side.