BUG Updated fieldgroup class and example code

Fieldgroup was being added twice to the parent class, also extraClass doesn't work for the fieldgroup anyway. Because the extraclass doesn't get added to the parent.

Added chosen.js support to dropdown in fieldgroup.

Before:

```
<div class="field fieldgroup fieldgroup">
	<label class="left">Champion</label>

	<div class="middleColumn fieldgroup ">
		<div class="fieldgroup-field first odd">
			<div class="fieldholder-small">
				<label class="fieldholder-small-label" for="Form_ItemEditForm_KampioenNaam">Champion name</label>
				<input type="text" name="KampioenNaam" class="text" id="Form_ItemEditForm_KampioenNaam"></div>
			</div>

			<div class="fieldgroup-field last even">
				<div class="fieldholder-small">

					<label class="fieldholder-small-label" for="Form_ItemEditForm_KampioenLand">Champion nationality</label>
					<option value="AF">Afghanistan</option>
				</select>
			</div>
		</div>
	</div>
</div>
```

After:

```
<div class="field fieldgroup">
	<label class="left">Champion</label>

	<div class="middleColumn fieldgroup">
		<div class="fieldgroup-field first odd">
			<div class="fieldholder-small">
				<label class="fieldholder-small-label" for="Form_ItemEditForm_KampioenNaam">Champion name</label>
				<input type="text" name="KampioenNaam" class="text" id="Form_ItemEditForm_KampioenNaam">
			</div>
		</div>

		<div class="fieldgroup-field last even">
			<div class="fieldholder-small">
				<label class="fieldholder-small-label" for="Form_ItemEditForm_KampioenLand">Champion nationality</label>

				<select name="KampioenLand" class="customcountrydropdown dropdown" id="Form_ItemEditForm_KampioenLand">
					<option value="AF">Afghanistan</option>
				</select>
			</div>
		</div>
	</div>
</div>
```