Add a setting to transform all XO errors to warnings

[flowstate247]

I like to distinguish linting problems from type errors while editing.
So I would prefer that all the rules would be shown as warnings, not errors.

[fregante]

https://github.com/bfanger/eslint-plugin-only-warn

Unfortunately there isn’t a way to do this in ESLint.

Alternatively I suggest altering your IDE to change how it deals with lint vs types (which sounds useful, honestly)