title: Trouble setting activeFocus to Item in a QML TabView
body: <p>When the user changes the current tab in my TabView. I would like to set the activeFocus to the top level Item in the current tab, e.g. using forceActiveFocus. However for some weird reason the TabView is setting the activeFocus to the first Button it finds in the Tab, even if that Button has "focus: false" set. 
  As shown in the output below. When I use forceActiveFocus to set the focus to the top-level Item. First that Item gets focus, then it immediately loses focus and the Button gains focus instead. If there is no Button in the tab, then it works as expected. I need advice on a work-around for this problem. I would like to know if this is a Bug or whether I'm doing something wrong here?</p>
  
  <p>Below is the program output when the user clicks on the 2nd tab.</p>
  
  <pre><code>qml: Item Focus gained: Tab2
  qml: Button focus gained: Tab2
  qml: Item Focus lost: Tab2
  </code></pre>
  
  <p>Code example follows (tested in Qt 5.4.2):</p>
  
  <pre><code>import QtQuick 2.4
  import QtQuick.Controls 1.3
  import QtQuick.Window 2.2
  import QtQuick.Dialogs 1.2
  
  ApplicationWindow {
      width: 640
      height: 480
      visible: true
  
      TabView {
          id: tabView
  
          onCurrentIndexChanged: {
              getTab(currentIndex).forceActiveFocus();
          }
      }
  
      Component.onCompleted: {
          var tab1 = tabView.addTab("tab1", tabComp);
          tab1.active = true;
          tab1.item.objectName = "Tab1";
  
          var tab2 = tabView.addTab("tab2", tabComp);
          tab2.active = true;
          tab2.item.objectName = "Tab2";
      }
  
      Component {
          id: tabComp
          Item {
              focus: true
              onActiveFocusChanged: {
                  if(activeFocus)
                      console.log("Item Focus gained: " + objectName);
                  else
                      console.log("Item Focus lost: " + objectName);
              }
  
              Button {
                  focus: false
                  onActiveFocusChanged: {
                      if(activeFocus)
                          console.log("Button focus gained: " + parent.objectName);
                      else
                          console.log("Button focus lost: " + parent.objectName);
                  }
              }
          }
      }
  }
  </code></pre>