[Cin] Imported sequences in Master Project and the Viewer

[Andrea paz]

Done. On my own initiative, I changed the title and put a subtitle on
it; but further changes are always possible.

https://www.dropbox.com/s/0js49r47s0qu621/CinelerraGG_Manual.pdf?dl=0

@Igor
> On the manual, in "Camera and Projector" section, I think it would be
> important to add the two images that you find in "Cinelerra CV Manual.htm"
> and I add here. I know, they are drawn by hand but it is important to
> understand how camera and projector work.
Igor, you (or others) could redraw them in Inkscape or even Blender. I
don't think the original author cares.