Separate python dependencies into optional groups

Some project dependencies are only needed for the web page, some are only needed during training, etc. It could be worth breaking the dependency list into groups so that users don't need to install all of them just to get started with using the repo

```
[project.optional-dependencies]
data_prep = [
    "img2dataset"
]
web_demo = [
    ...
]
training = [
   ...
]
```