Support multiple video streams for video input. VideoInput interface still backwards compatible.
Update V4L to support multiple streams too. Untested.
Experimental image capture interface. Use ImageDims struct for parsing video uri.

Signed-off-by: Steven Lovegrove <stevenlovegrove@gmail.com>
Add video splitter for turning a single stream video into a multiple stream video based on ROI.

Signed-off-by: Steven Lovegrove <stevenlovegrove@gmail.com>