Configuration variable for wildcard_imports to always warn

[dylni]

Suggested on this pull request:

Since wildcard_imports is starting to warn in less cases, should it have a configuration variable to always warn? That would also help make the documentation clearer about it not warning in all cases by default.

It would be helpful if a configuration variable is added to wildcard_imports that skips checking for:

• importing in a macro
• importing the prelude
• importing in tests

This might be a good first issue.