[FEATURE query-params] Allow link-to helper to work without route

Someone asked in IRC and I've been meaning to implement for a while anyway, this allows:

```javascript
App.Router.map(function() {
  this.route('index', {queryParams: ['page']});
});
```

```handlebars
{{#link-to page=2}}Next Page{{/link-to}}
```

This is useful for example in components that can be used on multiple routes (a pagination component would be a good example) that want to change the query params but don't care about the actual route that is active.