Implements native UI for preferences editing. In particular, the API
handles the differences between modal (Windows) and non-modal (OS X) preferences windows and provides platform's native look.
Currently implemented natively for wxOSX/Cocoa, wxGTK and Windows (the latter is used as a fallback generic implementation as well).
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73576 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
