Make the content item the default one.

To make the addition of the qml docs more prominent, make the content
item the default one as it shows all available documentation sets.

Task-number: QTCREATORBUG-1024
Reviewed-by: kkoehne

src/plugins/help/helpplugin.cpp

@@ -428,7 +428,7 @@ void HelpPlugin::setupUi()
     itemList << m_contentItem << m_indexItem << m_searchItem << m_bookmarkItem
         << m_openPagesItem;
     m_sideBar = new Core::SideBar(itemList, QList<Core::SideBarItem*>()
-        << m_indexItem << m_openPagesItem);
+        << m_contentItem << m_openPagesItem);
     m_sideBar->setShortcutMap(shortcutMap);
 
     m_splitter->setOpaqueResize(false);