Support override of JsTree options from widget

[lennartvdd]

For more flexibility I thought it would be nice to be able to set any JsTree option directly when calling the widget in a view, so i've added an $options attribute to the JsTreeWidget class.
Any options set there will be merged to the default options defined in js_plugins/jstree.behavior.js using JQuery's $.extend(true, {}, {});, meaning if you define JsTreeWidget::$options, the defaults will not be lost, but can only be overriden or extended.

Example:

<?php
$this->widget('application.widgets.JsTreeWidget', array(
    #...
    'options' => array(
        'html_data'=>array(
            'ajax' => array(
                'url' => $this->createUrl('fetchTree', array('id' => $_GET['id'])),
            ),
        ),
        'types' => array(
            'max_children' => 1,
        ),
    ),
    #...
));
?>