[Search] Inject id and class attr into individual result

[dreaming-augustin]

Give much more flexibility on the type of content and theming possibilities for each individual search result.

We could already manipulate the response received by the Search API:

onResponse: function(original_response) {
    var response = {
       results : {}
    };
    $.each(original_response.results, function(index, item) {
          // Manipulate each item.
          // Possibly add item.id
         // Possibly add item.classes
    }
    return response;
}

The problem is that we couldn't inject the id and class attributes to each individual item rendered by the Search module.

Now, depending on the status of each response, the status potentially reflecting a given website's logic and needs, we can inject an id and additional classes that can then be used for theming and manipulating.

Also, before each item was wrapped within a <a> tag. Because HTML prohibits having nested <a> tags (which makes sense), we couldn't inject any link into the body of individual items (e.g. inject relevant links to open in a different browser tab, while keeping the result popup menu open).

Now, if the result item has result[fields.url], then keep the <a> tag, because it makes sense: the whole result is assigned an URL.
If result[fields.url] is absent, the result is wrapped within a <div> tag, making it possible to inject one or even several links into the result's description, as may be required.

This feature is backward-compatible, as the default behavior is unchanged.

[dreaming-augustin]

If requested, I can submit a PR for documentation later.

[dreaming-augustin]

Here are two examples of theming achieved with this new feature: