title: MVVMCross with multiple types of CollectionViewCell and data binding issue
body: <p>I'm new to MVVMCross, theoretically it's shouldn't be that hard until I started using UICollectionViewCell</p>
  
  <p>I have multiple sections in my view controller, and each of them should bind to different types of data, what should I do?</p>
  
  <p>in the ViewModel, it has a list and a property I want to use the following properties to fill my custom cells</p>
  
  <pre><code>List&lt;ClassForCell1&gt; list;
  private int _valueForCell2;
  
  public int ValueForCell2
  {
      get =&gt; _valueForCell2;
      set =&gt; _valueForCell2 = value;
  }
  </code></pre>
  
  <p>In MySource class, I registered different types of Cell, which looks like this</p>
  
  <pre><code>public MySource(UICollectionView collectionView, ViewModel viewModel) : base(collectionView)
  {
      _viewModel = viewModel;
      collectionView.RegisterClassForCell(typeof(CustomCell1), CustomCell1.Key);
      collectionView.RegisterNibForCell(CustomCell2.Nib, CustomCell2.Key);
      //... some other cell registration
  }
  </code></pre>
  
  <p>Here are my Cells</p>
  
  <pre><code>protected CustomCell1(IntPtr handle) : base(handle)
  {
      this.DelayBind(() =&gt;
      {
          var set = this.CreateBindingSet&lt;CustomCell1, ClassForCell1&gt;();
          set.Bind(NameLabel).To(m =&gt; m.name);
          set.Apply();
      });
  }
  
  protected CustomCell2(IntPtr handle) : base(handle)
  {
      this.DelayBind(() =&gt;
      {
          // how to bind this one?
          var set = this.CreateBindingSet&lt;CustomCell2, ???&gt;();
          set.Bind(NameLabel).To(a view model's value); // ValueForCell2 in ViewModel
          set.Apply();
      });
  }
  </code></pre>
  
  <p>My questions are:</p>
  
  <ol>
  <li>How can I bind viewModel's specific property or list to the specific cell(s) or section(s)? </li>
  </ol>
  
  <p>here's the code snippet in my ViewController, in order to bind ViewController and ViewModel, and it seems like doesn't work at all</p>
  
  <pre><code>var source = new MySource(MyCollectionView, MyViewModel);
  var set = this.CreateBindingSet&lt;MyViewController, MyViewModel&gt;();
  </code></pre>
  
  <ol start="2">
  <li>For CustomCell2, how to bind a label's Text property to view model's property? (ValueForCell2)</li>
  </ol>