Generate a data loader file from a cell

**Idea:**
Be able to define a data loader cell. For example:

~~~
```.py {name: requests.csv}
import requests
resp = results.get("https://random.com")
```
~~~

This will automatically generate a `requests.csv.py` file with the code and attempt to run it. It would be really cool if updating the code in `requests.csv.py` will reflect in this code block, but that sounds complicated...
