Use backbone.js for Contactlist

This replaces the current presenter/view classes for the contact/whoami components on the left with backbone views. Since I reuse my self-made models the business logic stays the same mostly.

Because of the non-backbone models there is an ugly points / work-around:
 * When removing a contact, the ContactView triggers an event which is captured by ContactRosterView, which then removes the contact from the roster. That should be done by a proper collection object.
 
Additional (required) changes:
 * I updated underscore.js + min
 * I added backbone.js + min