fix bugs and improve the approach making frames (#900)

1.  fix the bugs originated from the latest commit b544241f (Add support for all other (except KerasLatent) models: (autorope#884))

2.  improve the approach for calculating saliency maps,
2.1 evaluate the effects of all output layers instead of one
2.2 correct the problematic math (blending the gradients of angle and throttle output layers together) from direct sum to square norm
2.3 calculate the saliency depending on the model type "linear" and "categorical"

3.  modify the "draw_user_input", "draw_model_prediction", and "draw_steering_distribution" methods, seperate the image array for inference and the image array that labels are drawn on