Read up state from URL

@davidpfahler What do you think about reading `state.data.up` right from the url?
When a state has more than 1 URL segment we could automatically assign length-1 as the up state (if it is a state name obv).

Example:
```js
    $stateProvider.state('customers', {
      url: '/customers',
      templateUrl: 'customers.htmll'
    }).state('customer', {
      url: '/customers/:id',
      templateUrl: 'customer.html'
    })
```

Rather than defining `data: { up: 'customers'}` on the customer state we can just read it from the URL.

It won't be right for all occasions, but probably for a lot. The rest can be defined just like it is now.