Bumped Backbone.js version to 1.0.0 in Scala zentasks example

Bumped Backbone.js from 0.5.3 to 1.0.0.

* Bumped Underscore.js to 1.5.1 because 1.4.3 or higher required
* Fixed main.coffee 
 * I renamed `@el` to `@$el` because `@el` isn't a jQuery object in 1.0.0
 * `AppRouter`'s routes doesn't work, they shouldn't start with "/" in 1.0.0