routes.js: add basic routing

Run the following command before you start your Meteor server.
`mrt add iron:router`

The code that allows for routing is present in `routes.js`. Here is the code:
```
this.route('addCard');
this.route('dashboard');
this.route('review');
this.route('addToReviewList');
this.route('cardsList');
this.route('usersList');
this.route('intro', {
  path: '/'
});
```

Navigate to [http://localhost:3000/addCard](http://localhost:3000/addCard) to have the `addCard` template render. (It appends itself to index.html.)

Navigate to [http://localhost:3000/dashboard](http://localhost:3000/dashboard) to render the `dashboard` template.

Navigate to [http://localhost:3000/](http://localhost:3000/) to render the `intro` template. Note the path is '/' in this case.

Here are two great resources about iron-router:
* https://github.com/EventedMind/iron-router/blob/devel/DOCS.md
* http://www.manuel-schoebel.com/blog/iron-router-tutorial