Bug 1015388 - [Contacts] Implement new startup loading events

I'll keep loadEnd where it is according to the explanation of the event:
'moz-app-loaded': Emitted when the application has been completely loaded, e.g. any relevant "below-the-fold" functionality has been injected into the DOM, been marked visible, and is ready for user interaction, and any required startup background processing has completed.

We agreed with Eli that displaying the contact list is one of the  main features  and we should consider that we finished when we display the first chunk of contacts. (As the rest will be loaded dynamically)