Added wx.aui.AuiMDIParentFrame and wx.aui.AuiMDIChildFrame, which
essentially implement the MDI interface using a normal wx.Frame and a
wx.aui.AuiNotebook.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@44105 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775