getIconType(icon) {
        const ext = this.getIconExt(icon);

        return ext === 'ico' ? 'x-icon' : ext;
    }
Returns the mime type (part after image/) of the favicon that will get served (not the stored one) 
@param {string} [icon]
@returns {'png' | 'x-icon' | 'jpeg'}
@description Takes a path and returns boolean value.