ImageConverterModule now outportals an 8-bit ThresholdImage

ImageConverterModule now outportals an 8-bit ThresholdImage, rather than a 16-bit image, based on Bill's suggestion.

Ben, you might want to double check the changes we made in vision. We did do some basic testing, and the logs suggested that robot was seeing things (including the ball) as it should.

ImageConverterModule only supports 1280x480 images as of now because the assembly method acquire_image_fast is not able to support any other sized image. Bill may help change the assembly method in the future, but this limitation is documented in the comments of ImageConverterModule's run_ method.