- prior code just waited a couple of seconds.
- this new code now starts asking for frames and will wait
  until a frame is return or a timeout happens
- Generally this is a more reliable and faster way to warm
  the camera; if it is going to work it will return a frame
  quickly.  So start up is faster.
- The warmup code also declares a better  error if the camera can't
  start; it raises the error in the camera part rather than
  downstream where the image is used or later in the pipeline.
  That makes it easier to diagnose what is going on.

- if the camera returns a None image the code would
  crash.  That could happen with the prior CISC camera
  if it did not start properly.  However, that error
  was confusing.
- Now this code will simply ignore an None image.

- added --debug flag. if this is passed to 'drive' command
  then debug window is shown.  Otherwise it does not.
- this fixes an issue when using a headless OS on the
  donkeycar; open cv cannot create a debug window and so crashes.

- this guarantees we can produce frames before the camera
  is used
- also detects if pygame is not installed and prints instructions

- if both a CSIC camera and a USB camera are connected then
  there will be more than one camera available
- The current code always just choose index 0
- This change allows the index to be chose with
  cfg.CAMERA_INDEX, which defaults to zero