Allow states without any views

As of 1.0.0-beta.3 the ng1 code does not allow a state without a view.

If a state does not have a template, default it to `<ui-view></ui-view>`\

This has the benefit of allowing an abstract state to be created without any (explicit) template.

```js
.state('foo', {
  abstract: true
}).state('foo.bar', {
  template: '<h1>bar</h1>'
});
```