make dwm installable

[jsta]

I created a setup.py file and the other necessary infrastructure to install dwm. The enables inference.py to be called from other locations besides the dwm source code folder. Happy to close this PR but I thought I'd share in case its useful to someone else.

dwm_inference --checkpoint_path checkpoints/cp.135.ckpt --image_path sample_data/image2.tif --save_path water_map.png

instead of

python inference.py --checkpoint_path checkpoints/cp.135.ckpt --image_path sample_data/image2.tif --save_path water_map.png