Add support for CSS modules to stylelint-config-bitcrowd

[pmeinhardt]

Currently stylelint-config-bitcrowd chokes when used on CSS modules.
More specifically, I'm currently using CSS modules (written in SCSS) that use the composes property.

The current workaround looks (somewhat) like this:

const config = require('stylelint-config-bitcrowd');

const rules = {
  ...config.rules,
  'order/properties-order': ['composes', ...config.rules['order/properties-order']],
  'property-no-unknown': [
    true,
    {
      ignoreProperties: ['composes'],
    },
  ],
};

module.exports = { ...config, rules };

I've also taken stylelint-config-css-modules for a spin. However, that completely overrode the @function, @if… and other rules.