title: Extend selection in NSCollectionView with Shift key
body: <p>I recently reviewed one of my Applications that I released a year ago.
  And I see that nowadays the <code>NSCollectionView</code> inside it has lost the selection functioning such as SHIFT + Select now it behaving as CMD + Select.</p>
  <p>(Secondary issue: I am also not getting a selection rectangle when dragging with the mouse.)</p>
  <p>Obviously I want this feature back, where using shift would expand the selection from the previously clicked cell to the shift-clicked cell.</p>
  <p>What have I done:</p>
  <pre><code>//NSCollectionView * _picturesGridView; //is my iVar
  
  //In initialization I have set my _picturesGridView as follows
  //Initializations etc are omitted -- (only the selection related code is here)
  [_picturesGridView setSelectable:YES];
  [_picturesGridView setAllowsMultipleSelection:YES];
  </code></pre>
  <p><strong>Question:</strong> Is there an easy way to get back this functionality? I don't see anything related in documentation and I couldn't find any solution on the internet.</p>
  <p><strong>Sub Question:</strong> If there is no easy way to achieve that -&gt; Should I go ahead and create my own <code>FancyPrefix##CollectionViewClass</code> and to reimplement this feature as I wish -- Or is it better to go over the existing <code>NSCollectionView</code> and force it to behave as I wish?</p>
  <p><strong>Sub Note:</strong> Well if I will find myself reimplementing it it will be light weight class that will just comply to my own needs -- I mean I will not mimic the entire <code>NSCollectionView</code> class.</p>
  <p><strong>P.S.</strong>
  I am able to select an item by clicking on it I am able to select multiple items only with CMD+Click or SHIFT+Click but the latter behaves exactly as CMD+Click which I don't want as well.</p>
  <p>As for the mouse Selection Rectangle - I didn't override any Mouse events. It is not clear why I don't have this functionality.</p>