Toggle: group toggle updates and accordion example

**Toggle**

* Group toggle code  now sets on/off CSS classes and data states on the grouped elements.
* event.target for details element clicks was referencing the nested summary element.  Fixed by passing reference to clicked details element.
* Added Accordion example using group toggle

**Details**

* New `toggle.wb-details` event allows toggle plugin to open/close polyfilled details elements without triggering a summary click.
* Events that open/close details elements are now allowed to propagate.

**Breaking change**
The group toggle `data.group` property now expects a full CSS selector:

```html
<!-- note the dot in .grouped -->
<button type="button" class="wb-toggle" data-toggle='{"group": ".grouped"}'>Example 1</button> 
```

/cc @masterbee