title: How to select multiple files and directories with QML FileDialog
body: <p>I'm begining with Qt 5.5.<br />
  I want to use QML as much as possible for UI matters.<br/>
  I need a file and directory picker that can select multiple objects, either files or directories.<br />
  <a href="http://doc.qt.io/qt-5/qfiledialog.html" rel="nofollow"><code>QFileDialog</code></a> is able to do so, and according to <a href="http://www.qtcentre.org/threads/34226-QFileDialog-select-multiple-directories?p=220108#post220108" rel="nofollow">this solution</a>, the <code>QFileDialog</code> needs to be set to non native.<br />
  According to <a href="http://doc.qt.io/qt-5/qml-qtquick-dialogs-filedialog.html" rel="nofollow">QML <code>FileDialog</code> documentation</a>, there's no way for the programmer to force the QML <code>FileDialog</code> object to be non native.</p>
  
  <p>Must I use C++ to handle this or is there a way to access the properties of the QML <code>FileDialog</code> in order to force the instanciation of an underlying <code>QFileDialog</code>, and then a way to access to this instance properties from QML in order to implement the solution in QML ?</p>