bootstrap alert widget

Added bootstrap alert widget.

Examples of use:

```
echo Alert::widget(array(
	'options' => array('class' => 'block'),
	'body' => '<h4>Test</h4><p>Nice Body here</p>'
));
```
And 
```
Alert::begin(array(
	'options' => array('class' => 'alert-success'),
     'closeButton' => array(
            'label' => '&times;'
        )
 ));

 echo 'Say hello...';

Alert::end();
```

closes #329