Update code to use ember 1.0 idioms and match getting started guide

 * Change names to more closely mirror the "getting started" guide at emberjs.com
 * Add insert element lifecycle hooks by using `.on('didInsertElement')`
 * Remove class name bound to nonexistent `buttonClass` property
 * Change order of getter and setter in allAreDone to match getting started guide
 * Use an outlet in 'todos' template and add 'todos/index' template.
 * Remove 'text-cleared' custom view action to match "Getting Started" guide
 * `isCompleted` property saves model when used as a setter
 * `allAreDone` property saves changes when used as a setter