Add grid function

[alexarje]

It is sometimes useful to create grid-based visualizations of a video file. I have found a code snippet that does this easily with any number of images, such as 3x3:

or 7x7:

Would be cool to add this to the toolbox as well.

[joachimpoutaraud]

Just added a new grid-based video preview to the toolbox, some documentation can be found here : grid-based video