Adds the adversarial example generating script (in adversarial_depth.py)
which takes in a DepthModelWrapper instance (in depth_model_wrapper.py),
which has methods to load and call predict on a depth model, and moves
adversarial code into a separate directory.

Removes line that suppresses logging, changes image paths to local
paths in adversarial_depth.py, changes loss printing to Python string
formatting, removes global variable, and adds usage example to
depth_model_wrapper.py.

Fixes gitignore paths that have been moved to the depthvisualizer
directory.