Support for car brands

[bcaure]

I tried search with following values:

search.setFilter(leboncoin.FILTERS.ALL)
        .setCategory("voitures")
        .setRegion("ile_de_france")
        .addSearchExtra('brand', ["0", "Bmw"]);

It throws error:

node_modules\leboncoin-api\lib\search.js:248
            searchLabel = searchId[0].value;
                                      ^

TypeError: Cannot read property 'value' of undefined

I think it comes from the "groups" intermediate property in subcategories.json, unless I miss something?

  "2": {
    "brand": {
      "groups": [
        {
          "label": "Marques Courantes",
          "values": [
            {
              "label": "Audi",
              "value": "Audi"
            },
...
        {
          "label": "Autres Marques",
          "values": [
            {
              "label": "Abarth",
              "value": "Abarth"
            },

I think "Marques Courantes" and "Autres Marques" could be merged to solve this.
Otherwise I've made a quickfix, let me know if you want a merge request.