Context Menu: Add backwards compatibility to js

1. Add backwards compatibility to kendo.contextmenu.js
- Add items configuration back in.  Either dataSource or items can be
used.  The items configuration will be deprecated in Kendo UI 2014 Q1.
Use dataSource instead.
- Allow animation to be configurable.  Support "slide" and "fade"
effects.  Default will be "slide".

2. Add reference to kendo.contextmenu.css in Index.html