Add support for multiple simultaneous resolution, color, and codec settings

[GregMefford]

It would be great to be able to configure multiple outputs with different resolution and color space.

For example in my https://github.com/GregMefford/omni_eye training project, we use the Picam video to both stream a video to a display and to use zbar to scan for barcodes in the image. Ideally, we would send high-resolution color video to the screen and low-resolution luma-only images to the barcode-scanner, so that it has to do less processing work.

Another example would be to have a lower resolution for video preview being displayed on a small screen and a higher resolution for video being streamed or captured to a file. Similarly, it might be useful to have the preview as an RGB bitmap and the full video encoded as H.264 or MJPEG.