Some refactoring to clean up cli_streams a little bit

[khabinov]

• Moved static methods of configuration out
• Changed return type of parse_image_size from boost::optional to streams::error_or
• Changed types of time_limit and frames_limit from long to int to avoid overflow in streams::take()
• Changed decode_image_frames(width, height, ...) to decode_image_frames(image_size, ...)

This refactoring should help with converting recorder to pool mode.