TypeAhead plugin

Added TypeAhead plugin. Trying to keep the simplicity of the code at the `Modal` widget. 

Examples of use: 

```
// with active form
<?php echo \yii\bootstrap\TypeAhead::widget(array(
	'form' => $form,
	'model' => $model,
	'attribute' => 'name',
	'pluginOptions' => array(
		'source' => array('ESP', 'USA')
	)
));?>
```
without 
```
<?php echo \yii\bootstrap\TypeAhead::widget(array(
	'name' => 'test',
	'pluginOptions' => array(
		'source' => array('ESP', 'USA')
	)
));?>
```
closes #327