replace PIL with Pillow because PIL is kinda deprecated and is a pain to install

replace PIL with Pillow 

#### What's this PR do?
- replaces `PIL` with `Pillow`

#### Why am I doing this?  How does this help us?
- `PIL` is deprecated. Other projects use this as a library and have to install `PIL`. They end up having to do silly things like `pip install --allow-unverified PIL -r requirements.txt`

#### How should this be manually tested?
`python manage.py test`.  Not sure what else. 

### Next steps:
- remove `--allow-unverified PIL` from downstream projects