use Yii formatted URL

[cornernote]

also slight changes in widgets/JsTreeWidget.php:

• rename Yii_js.csrf to JsTreeBehavior.csrfToken
• remove Yii_js (its empty now)
• use json_encode() to format the entire JsTreeBehavior array
• only call Yii::app()->clientScript once, then assign to variable

fixes issue #7

[kabasakalis]

Your extension is great,and I am happy you used and adapted my extension for your needs.I also use it for menu management in my CMS.I appreciate your contribution,the problem is I cannot merge without testing this all.If something breaks I will have tenths of issues in Github complaining.And frankly,I have no time to test this.I am also focusing on Yii2 right now,I don't want to invest time in Yii1 extensions.And since there's no bug ,just an enhancement,I'd better leave my extension as is.I hope you understand.Great job!

[cornernote]

Yes I understand. The issue is fixed for all purposes I require, so if we can just leave this pull request open for anyone else who encounters the problem that should be enough.

[kabasakalis]

Sure,I'll leave it open!Thanks!