Fix render of "reset" and "button" in inline form

In inline form, the "reset" and "button" type of Buttons don´t need all the extra markup, just the <button> tag with all the inner add-ons.
With this fix, we can also print group buttons. Example:
class GroupButtonsFieldset extends Fieldset{

	public function __construct($name = null, $options = array()) {
		parent::__construct($name, $options);
		$this->add(array(
			'name' => 'save',
			'type' => 'Button',
			'options' => array(
				'label' => 'Save new',
				'glyphicon' => 'floppy-disk',
				'twb-layout' => 'inline'
			),
			'attributes' => array(
				'type' => 'submit',
				'value' => 'save',
				'class' => 'btn btn-success'
			),
		));
		$this->add(array(
			'name' => 'reset',
			'type' => 'Button',
			'options' => array(
				'label' => 'Reset',
				'glyphicon' => 'refresh',
				'twb-layout' => 'inline'
			),
			'attributes' => array(
				'type' => 'reset',
				'class' => 'btn btn-warning'
			),
		));

		$this->add(array(
			'name' => 'generic-button',
			'type' => 'Button',
			'options' => array(
				'label' => 'Back to list',
				'glyphicon' => 'arrow-left',
				'twb-layout' => 'inline'
			),
			'attributes' => array(
				'type' => 'button',
				'class' => 'btn'
			),
		));
	}
}