[feat] Support premade-whitelist

[qcoumes]

It would be great if premade whitelist could be added into vulture itself and given as an argument.

This would allow support for common frameworks such as Django or Flask, which by their nature give a lot of false positives.

As an example, pydocstyle do something related with its convention argument.

[jendrikseipp]

We already collect whitelists for common Python modules in the repo.