Implement wxCheckListBox based on wxListBox (wxQT)

Solution taken from wxGTK (but overriden Init private method to set m_hasCheckBoxes)
Use wxCheckListBox in controls sample

Replaced wxListBox with wxCheckListBox to test this derived class.
The behavior will be similar as in most platforms it is just based on wxListBox
Implement IsChecked / Check for wxCheckListBox in wxQT
Test methods of wxCheckListBox in controls sample

 * Add a toggle check button that call wxCheckListBox::Check
 * Show (in the log) the wxCheckListBox::IsCheck status when a item is selected