Starting to get familiar with angular.

We want to have an app that defines models based on the objects
exposed from the PT version 4 API:
https://www.pivotaltracker.com/help/api?version=v4

The models we want to define:
Users
Projects
Iterations(we will call them Sprints)
Stories
Comments
Tasks

This commit is the first step and defines the app, and the User
controller.