title: Overriding ViewModelStore
body: <p>Is it possible to provide once own implementation of a <code>ViewModelStore</code> for <code>ViewModelProviders</code> to use instead of the default one?</p>
  
  <p>More precisely, I'm interested in adding <code>fun clear(vm: ViewModel)</code> (or using an index or something similar) functionality to the <code>ViewModelStore</code> so that I can clear a single view model of my choice, not just use the built in <code>ViewModelStore#clear</code>:</p>
  
  <pre><code>public final void clear() {
      for (ViewModel vm : mMap.values()) {
          vm.onCleared();
      }
      mMap.clear();
  }
  </code></pre>
  
  <p>which clears all view models.</p>