Create plugin that looks up package info from an upstream repo

It would be nice to have a plugin that would look up package info from the upstream repo for detected packages with no package info.

In the case of a Python requirements.txt, this file contains something that looks like this:
```
flit==3.0.0
simplejson==1.0.0
```

We would enhance the Python package plugin to parse a `requirements.txt` file and then look up the package info based on the detected name and version of each dependency listed in `requirements.txt` and return license, copyright, and other data for that package. This saves us time by not having to open the `requirements.txt` file and looking up the info ourselves, and manually entering the data into our worksheet. With a plugin like this, we can collect all missing package data, then dump the data to the csv or other output without having to look up the packages manually.