Move ember-debug code to ES6

[teddyzeenny]

Refactor ember-debug:

• Replace all var with const and let
• Use arrow function for callbacks (instead of using the self/bind approach)
• Use destructuring to import Ember classes: const { RSVP, computed, run, Route } = Ember.
• Use the new method definition syntax in object literals: { foo() {} }

Part of #360

[Mawaheb]

This is almost complete, will raise a PR soon.

[teddyzeenny]

Done in #387