Adds svg-react-loader to gatsby webpack config (and removes svgs from the built-in url-loader config).

include and exclude plugin options can be specified, if either is present then svg-react-loader will use them and url-loader will be reenabled with the inverse.

The following uses svg-react-loader to process svgs from a path matching /assets/, and url-loader to process svgs from everywhere else.

{
    resolve: 'gatsby-plugin-react-svg',
    options: {
        include: /assets/
    }
}