1. added SetSelection() to wxItemContainer and removed its declarations

1. added SetSelection() to wxItemContainer and removed its declarations
   from derived classes
2. made wxItemContainer::Select() non virtual: it simply calls SetSelection()
3. renamed wxListBox::SetSelection(n, select) to DoSetSelection() for all
   ports and defined non virtual SetSelection() overloads in the base class
   to avoid virtual functions hiding

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@32004 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775