Contextual alternative options for accordion (collapse js)

Just like other components, accordion should has it self contextual alternatives.

#### Usage:

Just add a contextual class to `accordion-group`, a contextual class uses with prefix `accordion-*` (`*` stands for `primary`, `success`, `warning`, `danger`, `info`).
```html
<div class="accordion" id="accordion2">
  <div class="accordion-group accordion-info">
    <div class="accordion-heading">
      <a class="accordion-toggle" data-toggle="collapse" data-parent="#accordion2" href="#collapseOne">
        Collapsible Group Item #1
      </a>
    </div>
    <div id="collapseOne" class="accordion-body collapse in">
      <div class="accordion-inner">
        ...
      </div>
    </div>
  </div>
```

Demo available here : http://app.phgcode.com/app/google-search/284815942