Add code actions to add/remove/sort imports

[tomv564]

A sort imports action could always be available.
An add/remove import action could be registered for locations where pyflakes complained about missing/unused imports.

See: https://github.com/alecthomas/importmagic for a library supporting this functionality.

[gatesn]

Feel free to steal and build off https://github.com/palantir/python-language-server/tree/ngates/auto-import if you have time.

It's a little too rough right now. Ideally we would want import magic to report the position it found the unimported modules instead of searching for them :/

[ghost]

+1, import magic and isort combo would be amazing. I would probably leave isort as a separate manual command (same as YAPF).

[ghost]

To clarify, having a separate isort command would allow the user to clean the imports manually, not only when new ones are added automatically.

[ghost]

+1 for including importmagic! There are atom and vscode implementations already, guess it should be easy?

[zewa666]

any updates on this one?

[youben11]

@zewa666 implemented in #685. You can start testing if you'd like and report any issue that may arise.