Make wxWindow::SetSizeHints() do nothing.

  Make wxWindow::SetSizeHints() do nothing.
  Make wxTLW::SetSizeHints() set the various m_minWidth etc. fields.
  Override SetSizeHints() in wxGTK to call the relevant gtk funcion
    only there and not in every resize.
  Make GetMinWidth() etc. non-virtual.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42646 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775