title: NSPopover show relative to NSStatusItem
body: <p>This is my code:</p>
  
  <pre><code>if #available(OSX 10.10, *) {
      if let b = statusItem.button {
          popover.showRelativeToRect(b.bounds, ofView: b, preferredEdge: .MinY)
      }
  } else {
  }
  </code></pre>
  
  <p>The <code>else</code> block is for OS X Mavericks because <code>NSStatusItem.button</code> is not available. Is there a simple way of showing the popover relative to the status item? If not, is it possible to show the popover in the center of the screen instead without the arrow?</p>