Get rid of ugly wxCONTROL_ITEMCONTAINER_CLIENTDATAOBJECT_RECAST macro.

Replace it with wxWindowWithItems<> template class which takes care of
disambiguating between the two inherited Get/SetClientXXX() versions and use
it as a base class in all clases that previously used the macro.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68460 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775