title: Keep query strings when navigating between child routers
body: <p>Here's my child router and the view code:</p>
  
  <pre><code>router.createChildRouter().makeRelative({
    moduleId: 'products',
    fromParent: true,
    dynamicHash: ':id'
  }).map([
    { route: 'specs', title: 'Specs', moduleId: 'specs', nav: true },
    { route: 'reviews', title: 'Reviews', moduleId: 'reviews', nav: true }
  ]).buildNavigationModel();
  
  &lt;ul class="tabs" data-bind="foreach: router.navigationModel()"&gt;
     &lt;li data-bind="css: { selected: isActive }"&gt;&lt;a href="{{dynamicHash}}"&gt;{{title}}&lt;/a&gt;&lt;/li&gt;
  &lt;/ul&gt;
  </code></pre>
  
  <p>which will produce two tabs with the following URLs:</p>
  
  <ul>
  <li><code>example.com/#products/200/specs</code></li>
  <li><code>example.com/#products/200/reviews</code></li>
  </ul>
  
  <p>I have a toolbar on my reviews page that sorts the content by date or by rating, so the URL becomes:</p>
  
  <ul>
  <li><code>example.com/#products/200/reviews?date=asc&amp;rating=desc</code></li>
  </ul>
  
  <p>But when I switch tabs and come back, I lose the query strings. Is there way to keep them in the URL until I clear the filters?</p>